1 | <div align="center">
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2 | <br>
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3 | <br>
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4 | <img src="media/logo.svg" alt="type-fest" height="300">
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5 | <br>
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6 | <br>
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7 | <b>A collection of essential TypeScript types</b>
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8 | <br>
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9 | <br>
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10 | <br>
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11 | <br>
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12 | <div align="center">
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13 | <p>
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14 | <p>
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15 | <sup>
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16 | <a href="https://github.com/sponsors/sindresorhus">Sindre Sorhus' open source work is supported by the community</a>
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17 | </sup>
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18 | </p>
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19 | <sup>Special thanks to:</sup>
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20 | <br>
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21 | <br>
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22 | <a href="https://standardresume.co/tech">
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23 | <img src="https://sindresorhus.com/assets/thanks/standard-resume-logo.svg" width="180"/>
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24 | </a>
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25 | </p>
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26 | </div>
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27 | <br>
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28 | <hr>
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29 | </div>
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30 | <br>
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31 | <br>
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32 |
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33 | [![](https://img.shields.io/badge/unicorn-approved-ff69b4.svg)](https://giphy.com/gifs/illustration-rainbow-unicorn-26AHG5KGFxSkUWw1i)
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34 | [![npm dependents](https://badgen.net/npm/dependents/type-fest)](https://www.npmjs.com/package/type-fest?activeTab=dependents) [![npm downloads](https://badgen.net/npm/dt/type-fest)](https://www.npmjs.com/package/type-fest)
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35 |
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36 | Many of the types here should have been built-in. You can help by suggesting some of them to the [TypeScript project](https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md).
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37 |
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38 | Either add this package as a dependency or copy-paste the needed types. No credit required. 👌
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39 |
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40 | PR welcome for additional commonly needed types and docs improvements. Read the [contributing guidelines](.github/contributing.md) first.
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41 |
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42 | ## Install
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43 |
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44 | ```
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45 | $ npm install type-fest
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46 | ```
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47 |
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48 | *Requires TypeScript >=3.4*
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49 |
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50 | ## Usage
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51 |
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52 | ```ts
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53 | import {Except} from 'type-fest';
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54 |
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55 | type Foo = {
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56 | unicorn: string;
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57 | rainbow: boolean;
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58 | };
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59 |
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60 | type FooWithoutRainbow = Except<Foo, 'rainbow'>;
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61 | //=> {unicorn: string}
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62 | ```
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63 |
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64 | ## API
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65 |
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66 | Click the type names for complete docs.
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67 |
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68 | ### Basic
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69 |
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70 | - [`Primitive`](source/basic.d.ts) - Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).
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71 | - [`Class`](source/basic.d.ts) - Matches a [`class` constructor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes).
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72 | - [`TypedArray`](source/typed-array.d.ts) - Matches any [typed array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray), like `Uint8Array` or `Float64Array`.
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73 | - [`JsonObject`](source/basic.d.ts) - Matches a JSON object.
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74 | - [`JsonArray`](source/basic.d.ts) - Matches a JSON array.
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75 | - [`JsonValue`](source/basic.d.ts) - Matches any valid JSON value.
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76 | - [`ObservableLike`](source/basic.d.ts) - Matches a value that is like an [Observable](https://github.com/tc39/proposal-observable).
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77 |
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78 | ### Utilities
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79 |
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80 | - [`Except`](source/except.d.ts) - Create a type from an object type without certain keys. This is a stricter version of [`Omit`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-5.html#the-omit-helper-type).
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81 | - [`Mutable`](source/mutable.d.ts) - Create a type that strips `readonly` from all or some of an object's keys. The inverse of `Readonly<T>`.
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82 | - [`Merge`](source/merge.d.ts) - Merge two types into a new type. Keys of the second type overrides keys of the first type.
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83 | - [`MergeExclusive`](source/merge-exclusive.d.ts) - Create a type that has mutually exclusive keys.
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84 | - [`RequireAtLeastOne`](source/require-at-least-one.d.ts) - Create a type that requires at least one of the given keys.
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85 | - [`RequireExactlyOne`](source/require-exactly-one.d.ts) - Create a type that requires exactly a single key of the given keys and disallows more.
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86 | - [`PartialDeep`](source/partial-deep.d.ts) - Create a deeply optional version of another type. Use [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) if you only need one level deep.
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87 | - [`ReadonlyDeep`](source/readonly-deep.d.ts) - Create a deeply immutable version of an `object`/`Map`/`Set`/`Array` type. Use [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) if you only need one level deep.
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88 | - [`LiteralUnion`](source/literal-union.d.ts) - Create a union type by combining primitive types and literal types without sacrificing auto-completion in IDEs for the literal type part of the union. Workaround for [Microsoft/TypeScript#29729](https://github.com/Microsoft/TypeScript/issues/29729).
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89 | - [`Promisable`](source/promisable.d.ts) - Create a type that represents either the value or the value wrapped in `PromiseLike`.
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90 | - [`Opaque`](source/opaque.d.ts) - Create an [opaque type](https://codemix.com/opaque-types-in-javascript/).
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91 | - [`SetOptional`](source/set-optional.d.ts) - Create a type that makes the given keys optional.
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92 | - [`SetRequired`](source/set-required.d.ts) - Create a type that makes the given keys required.
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93 | - [`ValueOf`](source/value-of.d.ts) - Create a union of the given object's values, and optionally specify which keys to get the values from.
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94 | - [`PromiseValue`](source/promise-value.d.ts) - Returns the type that is wrapped inside a `Promise`.
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95 | - [`AsyncReturnType`](source/async-return-type.d.ts) - Unwrap the return type of a function that returns a `Promise`.
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96 | - [`ConditionalKeys`](source/conditional-keys.d.ts) - Extract keys from a shape where values extend the given `Condition` type.
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97 | - [`ConditionalPick`](source/conditional-pick.d.ts) - Like `Pick` except it selects properties from a shape where the values extend the given `Condition` type.
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98 | - [`ConditionalExcept`](source/conditional-except.d.ts) - Like `Omit` except it removes properties from a shape where the values extend the given `Condition` type.
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99 | - [`UnionToIntersection`](source/union-to-intersection.d.ts) - Convert a union type to an intersection type.
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100 | - [`Stringified`](source/stringified.d.ts) - Create a type with the keys of the given type changed to `string` type.
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101 | - [`FixedLengthArray`](source/fixed-length-array.d.ts) - Create a type that represents an array of the given type and length.
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102 | - [`IterableElement`](source/iterable-element.d.ts) - Get the element type of an `Iterable`/`AsyncIterable`. For example, an array or a generator.
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103 | - [`Entry`](source/entry.d.ts) - Create a type that represents the type of an entry of a collection.
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104 | - [`Entries`](source/entries.d.ts) - Create a type that represents the type of the entries of a collection.
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105 | - [`SetReturnType`](source/set-return-type.d.ts) - Create a function type with a return type of your choice and the same parameters as the given function type.
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106 | - [`Asyncify`](source/asyncify.d.ts) - Create an async version of the given function type.
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107 |
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108 | ### Template literal types
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109 |
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110 | *Note:* These require [TypeScript 4.1 or newer](https://devblogs.microsoft.com/typescript/announcing-typescript-4-1/#template-literal-types).
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111 |
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112 | - [`CamelCase`](ts41/camel-case.d.ts) – Convert a string literal to camel-case (`fooBar`).
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113 | - [`KebabCase`](ts41/kebab-case.d.ts) – Convert a string literal to kebab-case (`foo-bar`).
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114 | - [`PascalCase`](ts41/pascal-case.d.ts) – Converts a string literal to pascal-case (`FooBar`)
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115 | - [`SnakeCase`](ts41/snake-case.d.ts) – Convert a string literal to snake-case (`foo_bar`).
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116 | - [`DelimiterCase`](ts41/delimiter-case.d.ts) – Convert a string literal to a custom string delimiter casing.
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117 | - [`Get`](ts41/get.d.ts) - Get a deeply-nested property from an object using a key path, like [Lodash's `.get()`](https://lodash.com/docs/latest#get) function.
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118 |
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119 | ### Miscellaneous
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120 |
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121 | - [`PackageJson`](source/package-json.d.ts) - Type for [npm's `package.json` file](https://docs.npmjs.com/creating-a-package-json-file).
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122 | - [`TsConfigJson`](source/tsconfig-json.d.ts) - Type for [TypeScript's `tsconfig.json` file](https://www.typescriptlang.org/docs/handbook/tsconfig-json.html) (TypeScript 3.7).
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123 |
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124 | ## Declined types
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125 |
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126 | *If we decline a type addition, we will make sure to document the better solution here.*
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127 |
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128 | - [`Diff` and `Spread`](https://github.com/sindresorhus/type-fest/pull/7) - The PR author didn't provide any real-world use-cases and the PR went stale. If you think this type is useful, provide some real-world use-cases and we might reconsider.
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129 | - [`Dictionary`](https://github.com/sindresorhus/type-fest/issues/33) - You only save a few characters (`Dictionary<number>` vs `Record<string, number>`) from [`Record`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1429-L1434), which is more flexible and well-known. Also, you shouldn't use an object as a dictionary. We have `Map` in JavaScript now.
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130 | - [`SubType`](https://github.com/sindresorhus/type-fest/issues/22) - The type is powerful, but lacks good use-cases and is prone to misuse.
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131 | - [`ExtractProperties` and `ExtractMethods`](https://github.com/sindresorhus/type-fest/pull/4) - The types violate the single responsibility principle. Instead, refine your types into more granular type hierarchies.
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132 |
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133 | ## Tips
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134 |
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135 | ### Built-in types
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136 |
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137 | There are many advanced types most users don't know about.
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138 |
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139 | - [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) - Make all properties in `T` optional.
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140 | <details>
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141 | <summary>
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142 | Example
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143 | </summary>
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144 |
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145 | [Playground](https://www.typescriptlang.org/play/#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)
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146 |
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147 | ```ts
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148 | interface NodeConfig {
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149 | appName: string;
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150 | port: number;
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151 | }
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152 |
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153 | class NodeAppBuilder {
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154 | private configuration: NodeConfig = {
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155 | appName: 'NodeApp',
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156 | port: 3000
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157 | };
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158 |
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159 | private updateConfig<Key extends keyof NodeConfig>(key: Key, value: NodeConfig[Key]) {
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160 | this.configuration[key] = value;
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161 | }
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162 |
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163 | config(config: Partial<NodeConfig>) {
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164 | type NodeConfigKey = keyof NodeConfig;
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165 |
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166 | for (const key of Object.keys(config) as NodeConfigKey[]) {
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167 | const updateValue = config[key];
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168 |
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169 | if (updateValue === undefined) {
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170 | continue;
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171 | }
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172 |
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173 | this.updateConfig(key, updateValue);
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174 | }
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175 |
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176 | return this;
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177 | }
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178 | }
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179 |
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180 | // `Partial<NodeConfig>`` allows us to provide only a part of the
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181 | // NodeConfig interface.
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182 | new NodeAppBuilder().config({appName: 'ToDoApp'});
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183 | ```
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184 | </details>
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185 |
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186 | - [`Required<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1408-L1413) - Make all properties in `T` required.
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187 | <details>
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188 | <summary>
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189 | Example
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190 | </summary>
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191 |
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192 | [Playground](https://typescript-play.js.org/?target=6#code/AQ4SwOwFwUwJwGYEMDGNgGED21VQGJZwC2wA3gFCjXAzFJgA2A-AFzADOUckA5gNxUaIYjA4ckvGG07c+g6gF8KQkAgCuEFFDA5O6gEbEwUbLm2ESwABQIixACJIoSdgCUYAR3Vg4MACYAPGYuFvYAfACU5Ko0APRxwADKMBD+wFAAFuh2Vv7OSBlYGdmc8ABu8LHKsRyGxqY4oQT21pTCIHQMjOwA5DAAHgACxAAOjDAAdChYxL0ANLHUouKSMH0AEmAAhJhY6ozpAJ77GTCMjMCiV0ToSAb7UJPPC9WRgrEJwAAqR6MwSRQPFGUFocDgRHYxnEfGAowh-zgUCOwF6KwkUl6tXqJhCeEsxDaS1AXSYfUGI3GUxmc0WSneQA)
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193 |
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194 | ```ts
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195 | interface ContactForm {
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196 | email?: string;
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197 | message?: string;
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198 | }
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199 |
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200 | function submitContactForm(formData: Required<ContactForm>) {
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201 | // Send the form data to the server.
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202 | }
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203 |
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204 | submitContactForm({
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205 | email: 'ex@mple.com',
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206 | message: 'Hi! Could you tell me more about…',
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207 | });
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208 |
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209 | // TypeScript error: missing property 'message'
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210 | submitContactForm({
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211 | email: 'ex@mple.com',
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212 | });
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213 | ```
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214 | </details>
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215 |
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216 | - [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) - Make all properties in `T` readonly.
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217 | <details>
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218 | <summary>
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219 | Example
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220 | </summary>
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221 |
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222 | [Playground](https://typescript-play.js.org/?target=6#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)
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223 |
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224 | ```ts
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225 | enum LogLevel {
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226 | Off,
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227 | Debug,
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228 | Error,
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229 | Fatal
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230 | };
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231 |
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232 | interface LoggerConfig {
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233 | name: string;
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234 | level: LogLevel;
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235 | }
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236 |
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237 | class Logger {
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238 | config: Readonly<LoggerConfig>;
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239 |
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240 | constructor({name, level}: LoggerConfig) {
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241 | this.config = {name, level};
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242 | Object.freeze(this.config);
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243 | }
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244 | }
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245 |
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246 | const config: LoggerConfig = {
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247 | name: 'MyApp',
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248 | level: LogLevel.Debug
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249 | };
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250 |
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251 | const logger = new Logger(config);
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252 |
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253 | // TypeScript Error: cannot assign to read-only property.
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254 | logger.config.level = LogLevel.Error;
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255 |
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256 | // We are able to edit config variable as we please.
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257 | config.level = LogLevel.Error;
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258 | ```
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259 | </details>
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260 |
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261 | - [`Pick<T, K>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1422-L1427) - From `T`, pick a set of properties whose keys are in the union `K`.
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262 | <details>
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263 | <summary>
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264 | Example
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265 | </summary>
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266 |
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267 | [Playground](https://typescript-play.js.org/?target=6#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)
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268 |
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269 | ```ts
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270 | interface Article {
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271 | title: string;
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272 | thumbnail: string;
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273 | content: string;
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274 | }
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275 |
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276 | // Creates new type out of the `Article` interface composed
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277 | // from the Articles' two properties: `title` and `thumbnail`.
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278 | // `ArticlePreview = {title: string; thumbnail: string}`
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279 | type ArticlePreview = Pick<Article, 'title' | 'thumbnail'>;
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280 |
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281 | // Render a list of articles using only title and description.
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282 | function renderArticlePreviews(previews: ArticlePreview[]): HTMLElement {
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283 | const articles = document.createElement('div');
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284 |
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285 | for (const preview of previews) {
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286 | // Append preview to the articles.
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287 | }
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288 |
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289 | return articles;
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290 | }
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291 |
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292 | const articles = renderArticlePreviews([
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293 | {
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294 | title: 'TypeScript tutorial!',
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295 | thumbnail: '/assets/ts.jpg'
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296 | }
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297 | ]);
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298 | ```
|
---|
299 | </details>
|
---|
300 |
|
---|
301 | - [`Record<K, T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1429-L1434) - Construct a type with a set of properties `K` of type `T`.
|
---|
302 | <details>
|
---|
303 | <summary>
|
---|
304 | Example
|
---|
305 | </summary>
|
---|
306 |
|
---|
307 | [Playground](https://typescript-play.js.org/?target=6#code/AQ4ejYAUHsGcCWAXBMB2dgwGbAKYC2ADgDYwCeeemCaWArgE7ADGMxAhmuQHQBQoYEnJE8wALKEARnkaxEKdMAC8wAOS0kstGuAAfdQBM8ANzxlRjXQbVaWACwC0JPB0NqA3HwGgIwAJJoWozYHCxixnAsjAhStADmwESMMJYo1Fi4HMCIaPEu+MRklHj8gpqyoeHAAKJFFFTAAN4+giDYCIxwSAByHAR4AFw5SDF5Xm2gJBzdfQPD3WPxE5PAlBxdAPLYNQAelgh4aOHDaPQEMowrIAC+3oJ+AMKMrlrAXFhSAFZ4LEhC9g4-0BmA4JBISXgiCkBQABpILrJ5MhUGhYcATGD6Bk4Hh-jNgABrPDkOBlXyQAAq9ngYmJpOAAHcEOCRjAXqwYODfoo6DhakUSph+Uh7GI4P0xER4Cj0OSQGwMP8tP1hgAlX7swwAHgRl2RvIANALSA08ABtAC6AD4VM1Wm0Kow0MMrYaHYJjGYLLJXZb3at1HYnC43Go-QHQDcvA6-JsmEJXARgCDgMYWAhjIYhDAU+YiMAAFIwex0ZmilMITCGF79TLAGRsAgJYAAZRwSEZGzEABFTOZUrJ5Yn+jwnWgeER6HB7AAKJrADpdXqS4ZqYultTG6azVfqHswPBbtauLY7fayQ7HIbAAAMwBuAEoYw9IBq2Ixs9h2eFMOQYPQObALQKJgggABeYhghCIpikkKRpOQRIknAsZUiIeCttECBEP8NSMCkjDDAARMGziuIYxHwYOjDCMBmDNnAuTxA6irdCOBB1Lh5Dqpqn66tISIykawBnOCtqqC0gbjqc9DgpGkxegOliyfJDrRkAA)
|
---|
308 |
|
---|
309 | ```ts
|
---|
310 | // Positions of employees in our company.
|
---|
311 | type MemberPosition = 'intern' | 'developer' | 'tech-lead';
|
---|
312 |
|
---|
313 | // Interface describing properties of a single employee.
|
---|
314 | interface Employee {
|
---|
315 | firstName: string;
|
---|
316 | lastName: string;
|
---|
317 | yearsOfExperience: number;
|
---|
318 | }
|
---|
319 |
|
---|
320 | // Create an object that has all possible `MemberPosition` values set as keys.
|
---|
321 | // Those keys will store a collection of Employees of the same position.
|
---|
322 | const team: Record<MemberPosition, Employee[]> = {
|
---|
323 | intern: [],
|
---|
324 | developer: [],
|
---|
325 | 'tech-lead': [],
|
---|
326 | };
|
---|
327 |
|
---|
328 | // Our team has decided to help John with his dream of becoming Software Developer.
|
---|
329 | team.intern.push({
|
---|
330 | firstName: 'John',
|
---|
331 | lastName: 'Doe',
|
---|
332 | yearsOfExperience: 0
|
---|
333 | });
|
---|
334 |
|
---|
335 | // `Record` forces you to initialize all of the property keys.
|
---|
336 | // TypeScript Error: "tech-lead" property is missing
|
---|
337 | const teamEmpty: Record<MemberPosition, null> = {
|
---|
338 | intern: null,
|
---|
339 | developer: null,
|
---|
340 | };
|
---|
341 | ```
|
---|
342 | </details>
|
---|
343 |
|
---|
344 | - [`Exclude<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1436-L1439) - Exclude from `T` those types that are assignable to `U`.
|
---|
345 | <details>
|
---|
346 | <summary>
|
---|
347 | Example
|
---|
348 | </summary>
|
---|
349 |
|
---|
350 | [Playground](https://typescript-play.js.org/?target=6#code/JYOwLgpgTgZghgYwgAgMrQG7QMIHsQzADmyA3gFDLIAOuUYAXMiAK4A2byAPsgM5hRQJHqwC2AI2gBucgF9y5MAE9qKAEoQAjiwj8AEnBAATNtGQBeZAAooWphu26wAGmS3e93bRC8IASgsAPmRDJRlyAHoI5ABRAA8ENhYjFFYOZGVVZBgoXFFkAAM0zh5+QRBhZhYJaAKAOkjogEkQZAQ4X2QAdwALCFbaemRgXmQtFjhOMFwq9K6ULuB0lk6U+HYwZAxJnQaYFhAEMGB8ZCIIMAAFOjAANR2IK0HGWISklIAedCgsKDwCYgAbQA5M9gQBdVzFQJ+JhiSRQMiUYYwayZCC4VHPCzmSzAspCYEBWxgFhQAZwKC+FpgJ43VwARgADH4ZFQSWSBjcZPJyPtDsdTvxKWBvr8rD1DCZoJ5HPopaYoK4EPhCEQmGKcKriLCtrhgEYkVQVT5Nr4fmZLLZtMBbFZgT0wGBqES6ghbHBIJqoBKFdBWQpjfh+DQbhY2tqiHVsbjLMVkAB+ZAAZiZaeQTHOVxu9ySjxNaujNwDVHNvzqbBGkBAdPoAfkQA)
|
---|
351 |
|
---|
352 | ```ts
|
---|
353 | interface ServerConfig {
|
---|
354 | port: null | string | number;
|
---|
355 | }
|
---|
356 |
|
---|
357 | type RequestHandler = (request: Request, response: Response) => void;
|
---|
358 |
|
---|
359 | // Exclude `null` type from `null | string | number`.
|
---|
360 | // In case the port is equal to `null`, we will use default value.
|
---|
361 | function getPortValue(port: Exclude<ServerConfig['port'], null>): number {
|
---|
362 | if (typeof port === 'string') {
|
---|
363 | return parseInt(port, 10);
|
---|
364 | }
|
---|
365 |
|
---|
366 | return port;
|
---|
367 | }
|
---|
368 |
|
---|
369 | function startServer(handler: RequestHandler, config: ServerConfig): void {
|
---|
370 | const server = require('http').createServer(handler);
|
---|
371 |
|
---|
372 | const port = config.port === null ? 3000 : getPortValue(config.port);
|
---|
373 | server.listen(port);
|
---|
374 | }
|
---|
375 | ```
|
---|
376 | </details>
|
---|
377 |
|
---|
378 | - [`Extract<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1441-L1444) - Extract from `T` those types that are assignable to `U`.
|
---|
379 | <details>
|
---|
380 | <summary>
|
---|
381 | Example
|
---|
382 | </summary>
|
---|
383 |
|
---|
384 | [Playground](https://typescript-play.js.org/?target=6#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXzSwEdkQBJYACgEoAueVZAWwCMQYBuAKDDwGcM8MgBF4AXngBlAJ6scESgHIRi6ty5ZUGdoihgEABXZ888AN5d48ANoiAuvUat23K6ihMQ9ATE0BzV3goPy8GZjZOLgBfLi4Aejj4AEEICBwAdz54MAALKFQQ+BxEeAAHY1NgKAwoIKy0grr4DByEUpgccpgMaXgAaxBerCzi+B9-ZulygDouFHRsU1z8kKMYE1RhaqgAHkt4AHkWACt4EAAPbVRgLLWNgBp9gGlBs8uQa6yAUUuYPQwdgNpKM7nh7mMML4CgA+R5WABqUAgpDeVxuhxO1he0jsXGh8EoOBO9COx3BQPo2PBADckaR6IjkSA6PBqTgsMBzPsicdrEC7OJWXSQNwYvFEgAVTS9JLXODpeDpKBZFg4GCoWa8VACIJykAKiQWKy2YQOAioYikCg0OEMDyhRSy4DyxS24KhAAMjyi6gS8AAwjh5OD0iBFHAkJoEOksC1mnkMJq8gUQKDNttKPlnfrwYp3J5XfBHXqoKpfYkAOI4ansTxaeDADmoRSCCBYAbxhC6TDx6rwYHIRX5bScjA4bLJwoDmDwDkfbA9JMrVMVdM1TN69LgkTgwgkchUahqIA)
|
---|
385 |
|
---|
386 | ```ts
|
---|
387 | declare function uniqueId(): number;
|
---|
388 |
|
---|
389 | const ID = Symbol('ID');
|
---|
390 |
|
---|
391 | interface Person {
|
---|
392 | [ID]: number;
|
---|
393 | name: string;
|
---|
394 | age: number;
|
---|
395 | }
|
---|
396 |
|
---|
397 | // Allows changing the person data as long as the property key is of string type.
|
---|
398 | function changePersonData<
|
---|
399 | Obj extends Person,
|
---|
400 | Key extends Extract<keyof Person, string>,
|
---|
401 | Value extends Obj[Key]
|
---|
402 | > (obj: Obj, key: Key, value: Value): void {
|
---|
403 | obj[key] = value;
|
---|
404 | }
|
---|
405 |
|
---|
406 | // Tiny Andrew was born.
|
---|
407 | const andrew = {
|
---|
408 | [ID]: uniqueId(),
|
---|
409 | name: 'Andrew',
|
---|
410 | age: 0,
|
---|
411 | };
|
---|
412 |
|
---|
413 | // Cool, we're fine with that.
|
---|
414 | changePersonData(andrew, 'name', 'Pony');
|
---|
415 |
|
---|
416 | // Goverment didn't like the fact that you wanted to change your identity.
|
---|
417 | changePersonData(andrew, ID, uniqueId());
|
---|
418 | ```
|
---|
419 | </details>
|
---|
420 |
|
---|
421 | - [`NonNullable<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1446-L1449) - Exclude `null` and `undefined` from `T`.
|
---|
422 | <details>
|
---|
423 | <summary>
|
---|
424 | Example
|
---|
425 | </summary>
|
---|
426 | Works with <code>strictNullChecks</code> set to <code>true</code>. (Read more <a href="https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html">here</a>)
|
---|
427 |
|
---|
428 | [Playground](https://typescript-play.js.org/?target=6#code/C4TwDgpgBACg9gJ2AOQK4FsBGEFQLxQDOwCAlgHYDmUAPlORtrnQwDasDcAUFwPQBU-WAEMkUOADMowqAGNWwwoSgATCBIqlgpOOSjAAFsOBRSy1IQgr9cKJlSlW1mZYQA3HFH68u8xcoBlHA8EACEHJ08Aby4oKDBUTFZSWXjEFEYcAEIALihkXTR2YSSIAB54JDQsHAA+blj4xOTUsHSACkMzPKD3HHDHNQQAGjSkPMqMmoQASh7g-oihqBi4uNIpdraxPAI2VhmVxrX9AzMAOm2ppnwoAA4ABifuE4BfKAhWSyOTuK7CS7pao3AhXF5rV48E4ICDAVAIPT-cGQyG+XTEIgLMJLTx7CAAdygvRCA0iCHaMwarhJOIQjUBSHaACJHk8mYdeLwxtdcVAAOSsh58+lXdr7Dlcq7A3n3J4PEUdADMcspUE53OluAIUGVTx46oAKuAIAFZGQwCYAKIIBCILjUxaDHAMnla+iodjcIA)
|
---|
429 |
|
---|
430 | ```ts
|
---|
431 | type PortNumber = string | number | null;
|
---|
432 |
|
---|
433 | /** Part of a class definition that is used to build a server */
|
---|
434 | class ServerBuilder {
|
---|
435 | portNumber!: NonNullable<PortNumber>;
|
---|
436 |
|
---|
437 | port(this: ServerBuilder, port: PortNumber): ServerBuilder {
|
---|
438 | if (port == null) {
|
---|
439 | this.portNumber = 8000;
|
---|
440 | } else {
|
---|
441 | this.portNumber = port;
|
---|
442 | }
|
---|
443 |
|
---|
444 | return this;
|
---|
445 | }
|
---|
446 | }
|
---|
447 |
|
---|
448 | const serverBuilder = new ServerBuilder();
|
---|
449 |
|
---|
450 | serverBuilder
|
---|
451 | .port('8000') // portNumber = '8000'
|
---|
452 | .port(null) // portNumber = 8000
|
---|
453 | .port(3000); // portNumber = 3000
|
---|
454 |
|
---|
455 | // TypeScript error
|
---|
456 | serverBuilder.portNumber = null;
|
---|
457 | ```
|
---|
458 | </details>
|
---|
459 |
|
---|
460 | - [`Parameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1451-L1454) - Obtain the parameters of a function type in a tuple.
|
---|
461 | <details>
|
---|
462 | <summary>
|
---|
463 | Example
|
---|
464 | </summary>
|
---|
465 |
|
---|
466 | [Playground](https://typescript-play.js.org/?target=6#code/GYVwdgxgLglg9mABAZwBYmMANgUwBQxgAOIUAXIgIZgCeA2gLoCUFAbnDACaIDeAUIkQB6IYgCypSlBxUATrMo1ECsJzgBbLEoipqAc0J7EMKMgDkiHLnU4wp46pwAPHMgB0fAL58+oSLARECEosLAA5ABUYG2QAHgAxJGdpVWREPDdMylk9ZApqemZEAF4APipacrw-CApEgBogkKwAYThwckQwEHUAIxxZJl4BYVEImiIZKF0oZRwiWVdbeygJmThgOYgcGFYcbhqApCJsyhtpWXcR1cnEePBoeDAABVPzgbTixFeFd8uEsClADcIxGiygIFkSEOT3SmTc2VydQeRx+ZxwF2QQ34gkEwDgsnSuFmMBKiAADEDjIhYk1Qm0OlSYABqZnYka4xA1DJZHJYkGc7yCbyeRA+CAIZCzNAYbA4CIAdxg2zJwVCkWirjwMswuEaACYmCCgA)
|
---|
467 |
|
---|
468 | ```ts
|
---|
469 | function shuffle(input: any[]): void {
|
---|
470 | // Mutate array randomly changing its' elements indexes.
|
---|
471 | }
|
---|
472 |
|
---|
473 | function callNTimes<Fn extends (...args: any[]) => any> (func: Fn, callCount: number) {
|
---|
474 | // Type that represents the type of the received function parameters.
|
---|
475 | type FunctionParameters = Parameters<Fn>;
|
---|
476 |
|
---|
477 | return function (...args: FunctionParameters) {
|
---|
478 | for (let i = 0; i < callCount; i++) {
|
---|
479 | func(...args);
|
---|
480 | }
|
---|
481 | }
|
---|
482 | }
|
---|
483 |
|
---|
484 | const shuffleTwice = callNTimes(shuffle, 2);
|
---|
485 | ```
|
---|
486 | </details>
|
---|
487 |
|
---|
488 | - [`ConstructorParameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1456-L1459) - Obtain the parameters of a constructor function type in a tuple.
|
---|
489 | <details>
|
---|
490 | <summary>
|
---|
491 | Example
|
---|
492 | </summary>
|
---|
493 |
|
---|
494 | [Playground](https://typescript-play.js.org/?target=6#code/MYGwhgzhAECCBOAXAlqApgWQPYBM0mgG8AoaaFRENALmgkXmQDsBzAblOmCycTV4D8teo1YdO3JiICuwRFngAKClWENmLAJRFOZRAAtkEAHQq00ALzlklNBzIBfYk+KhIMAJJTEYJsDQAwmDA+mgAPAAq0GgAHnxMODCKTGgA7tCKxllg8CwQtL4AngDaALraFgB80EWa1SRkAA6MAG5gfNAB4FABPDJyCrQR9tDNyG0dwMGhtBhgjWEiGgA00F70vv4RhY3hEZXVVinpc42KmuJkkv3y8Bly8EPaDWTkhiZd7r3e8LK3llwGCMXGQWGhEOsfH5zJlsrl8p0+gw-goAAo5MAAW3BaHgEEilU0tEhmzQ212BJ0ry4SOg+kg+gBBiMximIGA0nAfAQLGk2N4EAAEgzYcYcnkLsRdDTvNEYkYUKwSdCme9WdM0MYwYhFPSIPpJdTkAAzDKxBUaZX+aAAQgsVmkCTQxuYaBw2ng4Ok8CYcotSu8pMur09iG9vuObxZnx6SN+AyUWTF8MN0CcZE4Ywm5jZHK5aB5fP4iCFIqT4oRRTKRLo6lYVNeAHpG50wOzOe1zHr9NLQ+HoABybsD4HOKXXRA1JCoKhBELmI5pNaB6Fz0KKBAodDYPAgSUTmqYsAALx4m5nC6nW9nGq14KtaEUA9gR9PvuNCjQ9BgACNvcwNBtAcLiAA)
|
---|
495 |
|
---|
496 | ```ts
|
---|
497 | class ArticleModel {
|
---|
498 | title: string;
|
---|
499 | content?: string;
|
---|
500 |
|
---|
501 | constructor(title: string) {
|
---|
502 | this.title = title;
|
---|
503 | }
|
---|
504 | }
|
---|
505 |
|
---|
506 | class InstanceCache<T extends (new (...args: any[]) => any)> {
|
---|
507 | private ClassConstructor: T;
|
---|
508 | private cache: Map<string, InstanceType<T>> = new Map();
|
---|
509 |
|
---|
510 | constructor (ctr: T) {
|
---|
511 | this.ClassConstructor = ctr;
|
---|
512 | }
|
---|
513 |
|
---|
514 | getInstance (...args: ConstructorParameters<T>): InstanceType<T> {
|
---|
515 | const hash = this.calculateArgumentsHash(...args);
|
---|
516 |
|
---|
517 | const existingInstance = this.cache.get(hash);
|
---|
518 | if (existingInstance !== undefined) {
|
---|
519 | return existingInstance;
|
---|
520 | }
|
---|
521 |
|
---|
522 | return new this.ClassConstructor(...args);
|
---|
523 | }
|
---|
524 |
|
---|
525 | private calculateArgumentsHash(...args: any[]): string {
|
---|
526 | // Calculate hash.
|
---|
527 | return 'hash';
|
---|
528 | }
|
---|
529 | }
|
---|
530 |
|
---|
531 | const articleCache = new InstanceCache(ArticleModel);
|
---|
532 | const amazonArticle = articleCache.getInstance('Amazon forests burining!');
|
---|
533 | ```
|
---|
534 | </details>
|
---|
535 |
|
---|
536 | - [`ReturnType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1461-L1464) – Obtain the return type of a function type.
|
---|
537 | <details>
|
---|
538 | <summary>
|
---|
539 | Example
|
---|
540 | </summary>
|
---|
541 |
|
---|
542 | [Playground](https://typescript-play.js.org/?target=6#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-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
|
---|
543 |
|
---|
544 | ```ts
|
---|
545 | /** Provides every element of the iterable `iter` into the `callback` function and stores the results in an array. */
|
---|
546 | function mapIter<
|
---|
547 | Elem,
|
---|
548 | Func extends (elem: Elem) => any,
|
---|
549 | Ret extends ReturnType<Func>
|
---|
550 | >(iter: Iterable<Elem>, callback: Func): Ret[] {
|
---|
551 | const mapped: Ret[] = [];
|
---|
552 |
|
---|
553 | for (const elem of iter) {
|
---|
554 | mapped.push(callback(elem));
|
---|
555 | }
|
---|
556 |
|
---|
557 | return mapped;
|
---|
558 | }
|
---|
559 |
|
---|
560 | const setObject: Set<string> = new Set();
|
---|
561 | const mapObject: Map<number, string> = new Map();
|
---|
562 |
|
---|
563 | mapIter(setObject, (value: string) => value.indexOf('Foo')); // number[]
|
---|
564 |
|
---|
565 | mapIter(mapObject, ([key, value]: [number, string]) => {
|
---|
566 | return key % 2 === 0 ? value : 'Odd';
|
---|
567 | }); // string[]
|
---|
568 | ```
|
---|
569 | </details>
|
---|
570 |
|
---|
571 | - [`InstanceType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1466-L1469) – Obtain the instance type of a constructor function type.
|
---|
572 | <details>
|
---|
573 | <summary>
|
---|
574 | Example
|
---|
575 | </summary>
|
---|
576 |
|
---|
577 | [Playground](https://typescript-play.js.org/?target=6#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-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
|
---|
578 |
|
---|
579 | ```ts
|
---|
580 | class IdleService {
|
---|
581 | doNothing (): void {}
|
---|
582 | }
|
---|
583 |
|
---|
584 | class News {
|
---|
585 | title: string;
|
---|
586 | content: string;
|
---|
587 |
|
---|
588 | constructor(title: string, content: string) {
|
---|
589 | this.title = title;
|
---|
590 | this.content = content;
|
---|
591 | }
|
---|
592 | }
|
---|
593 |
|
---|
594 | const instanceCounter: Map<Function, number> = new Map();
|
---|
595 |
|
---|
596 | interface Constructor {
|
---|
597 | new(...args: any[]): any;
|
---|
598 | }
|
---|
599 |
|
---|
600 | // Keep track how many instances of `Constr` constructor have been created.
|
---|
601 | function getInstance<
|
---|
602 | Constr extends Constructor,
|
---|
603 | Args extends ConstructorParameters<Constr>
|
---|
604 | >(constructor: Constr, ...args: Args): InstanceType<Constr> {
|
---|
605 | let count = instanceCounter.get(constructor) || 0;
|
---|
606 |
|
---|
607 | const instance = new constructor(...args);
|
---|
608 |
|
---|
609 | instanceCounter.set(constructor, count + 1);
|
---|
610 |
|
---|
611 | console.log(`Created ${count + 1} instances of ${Constr.name} class`);
|
---|
612 |
|
---|
613 | return instance;
|
---|
614 | }
|
---|
615 |
|
---|
616 |
|
---|
617 | const idleService = getInstance(IdleService);
|
---|
618 | // Will log: `Created 1 instances of IdleService class`
|
---|
619 | const newsEntry = getInstance(News, 'New ECMAScript proposals!', 'Last month...');
|
---|
620 | // Will log: `Created 1 instances of News class`
|
---|
621 | ```
|
---|
622 | </details>
|
---|
623 |
|
---|
624 | - [`Omit<T, K>`](https://github.com/microsoft/TypeScript/blob/71af02f7459dc812e85ac31365bfe23daf14b4e4/src/lib/es5.d.ts#L1446) – Constructs a type by picking all properties from T and then removing K.
|
---|
625 | <details>
|
---|
626 | <summary>
|
---|
627 | Example
|
---|
628 | </summary>
|
---|
629 |
|
---|
630 | [Playground](https://typescript-play.js.org/?target=6#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-SgfXlHqVUE4xiAA)
|
---|
631 |
|
---|
632 | ```ts
|
---|
633 | interface Animal {
|
---|
634 | imageUrl: string;
|
---|
635 | species: string;
|
---|
636 | images: string[];
|
---|
637 | paragraphs: string[];
|
---|
638 | }
|
---|
639 |
|
---|
640 | // Creates new type with all properties of the `Animal` interface
|
---|
641 | // except 'images' and 'paragraphs' properties. We can use this
|
---|
642 | // type to render small hover tooltip for a wiki entry list.
|
---|
643 | type AnimalShortInfo = Omit<Animal, 'images' | 'paragraphs'>;
|
---|
644 |
|
---|
645 | function renderAnimalHoverInfo (animals: AnimalShortInfo[]): HTMLElement {
|
---|
646 | const container = document.createElement('div');
|
---|
647 | // Internal implementation.
|
---|
648 | return container;
|
---|
649 | }
|
---|
650 | ```
|
---|
651 | </details>
|
---|
652 |
|
---|
653 | - [`Uppercase<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms every character in a string into uppercase.
|
---|
654 | <details>
|
---|
655 | <summary>
|
---|
656 | Example
|
---|
657 | </summary>
|
---|
658 |
|
---|
659 | ```ts
|
---|
660 | type T = Uppercase<'hello'>; // 'HELLO'
|
---|
661 |
|
---|
662 | type T2 = Uppercase<'foo' | 'bar'>; // 'FOO' | 'BAR'
|
---|
663 |
|
---|
664 | type T3<S extends string> = Uppercase<`aB${S}`>;
|
---|
665 | type T4 = T30<'xYz'>; // 'ABXYZ'
|
---|
666 |
|
---|
667 | type T5 = Uppercase<string>; // string
|
---|
668 | type T6 = Uppercase<any>; // any
|
---|
669 | type T7 = Uppercase<never>; // never
|
---|
670 | type T8 = Uppercase<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
---|
671 | ```
|
---|
672 | </details>
|
---|
673 |
|
---|
674 | - [`Lowercase<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms every character in a string into lowercase.
|
---|
675 | <details>
|
---|
676 | <summary>
|
---|
677 | Example
|
---|
678 | </summary>
|
---|
679 |
|
---|
680 | ```ts
|
---|
681 | type T = Lowercase<'HELLO'>; // 'hello'
|
---|
682 |
|
---|
683 | type T2 = Lowercase<'FOO' | 'BAR'>; // 'foo' | 'bar'
|
---|
684 |
|
---|
685 | type T3<S extends string> = Lowercase<`aB${S}`>;
|
---|
686 | type T4 = T32<'xYz'>; // 'abxyz'
|
---|
687 |
|
---|
688 | type T5 = Lowercase<string>; // string
|
---|
689 | type T6 = Lowercase<any>; // any
|
---|
690 | type T7 = Lowercase<never>; // never
|
---|
691 | type T8 = Lowercase<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
---|
692 | ```
|
---|
693 | </details>
|
---|
694 |
|
---|
695 | - [`Capitalize<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms the first character in a string into uppercase.
|
---|
696 | <details>
|
---|
697 | <summary>
|
---|
698 | Example
|
---|
699 | </summary>
|
---|
700 |
|
---|
701 | ```ts
|
---|
702 | type T = Capitalize<'hello'>; // 'Hello'
|
---|
703 |
|
---|
704 | type T2 = Capitalize<'foo' | 'bar'>; // 'Foo' | 'Bar'
|
---|
705 |
|
---|
706 | type T3<S extends string> = Capitalize<`aB${S}`>;
|
---|
707 | type T4 = T32<'xYz'>; // 'ABxYz'
|
---|
708 |
|
---|
709 | type T5 = Capitalize<string>; // string
|
---|
710 | type T6 = Capitalize<any>; // any
|
---|
711 | type T7 = Capitalize<never>; // never
|
---|
712 | type T8 = Capitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
---|
713 | ```
|
---|
714 | </details>
|
---|
715 |
|
---|
716 | - [`Uncapitalize<S extends string>`](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-1.html#template-literal-types) - Transforms the first character in a string into lowercase.
|
---|
717 | <details>
|
---|
718 | <summary>
|
---|
719 | Example
|
---|
720 | </summary>
|
---|
721 |
|
---|
722 | ```ts
|
---|
723 | type T = Uncapitalize<'Hello'>; // 'hello'
|
---|
724 |
|
---|
725 | type T2 = Uncapitalize<'Foo' | 'Bar'>; // 'foo' | 'bar'
|
---|
726 |
|
---|
727 | type T3<S extends string> = Uncapitalize<`AB${S}`>;
|
---|
728 | type T4 = T30<'xYz'>; // 'aBxYz'
|
---|
729 |
|
---|
730 | type T5 = Uncapitalize<string>; // string
|
---|
731 | type T6 = Uncapitalize<any>; // any
|
---|
732 | type T7 = Uncapitalize<never>; // never
|
---|
733 | type T8 = Uncapitalize<42>; // Error, type 'number' does not satisfy the constraint 'string'
|
---|
734 | ```
|
---|
735 | </details>
|
---|
736 |
|
---|
737 | You can find some examples in the [TypeScript docs](https://www.typescriptlang.org/docs/handbook/advanced-types.html#predefined-conditional-types).
|
---|
738 |
|
---|
739 | ## Maintainers
|
---|
740 |
|
---|
741 | - [Sindre Sorhus](https://github.com/sindresorhus)
|
---|
742 | - [Jarek Radosz](https://github.com/CvX)
|
---|
743 | - [Dimitri Benin](https://github.com/BendingBender)
|
---|
744 | - [Pelle Wessman](https://github.com/voxpelli)
|
---|
745 |
|
---|
746 | ## License
|
---|
747 |
|
---|
748 | (MIT OR CC0-1.0)
|
---|
749 |
|
---|
750 | ---
|
---|
751 |
|
---|
752 | <div align="center">
|
---|
753 | <b>
|
---|
754 | <a href="https://tidelift.com/subscription/pkg/npm-type-fest?utm_source=npm-type-fest&utm_medium=referral&utm_campaign=readme">Get professional support for this package with a Tidelift subscription</a>
|
---|
755 | </b>
|
---|
756 | <br>
|
---|
757 | <sub>
|
---|
758 | Tidelift helps make open source sustainable for maintainers while giving companies<br>assurances about security, maintenance, and licensing for their dependencies.
|
---|
759 | </sub>
|
---|
760 | </div>
|
---|