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1# @ampproject/remapping
2
3> Remap sequential sourcemaps through transformations to point at the original source code
4
5Remapping allows you to take the sourcemaps generated through transforming your code and
6"remap" them to the original source locations. Think "my minified code, transformed with babel and
7bundled with webpack", all pointing to the correct location in your original source code.
8
9With remapping, none of your source code transformations need to be aware of the input's sourcemap,
10they only need to generate an output sourcemap. This greatly simplifies building custom
11transformations (think a find-and-replace).
12
13## Installation
14
15```sh
16npm install @ampproject/remapping
17```
18
19## Usage
20
21```typescript
22function remapping(
23 map: SourceMap | SourceMap[],
24 loader: (file: string) => (SourceMap | null | undefined),
25 options?: { excludeContent: boolean, decodedMappings: boolean }
26): SourceMap;
27```
28
29`remapping` takes the final output sourcemap, and a `loader` function. For every source file pointer
30in the sourcemap, the `loader` will be called with the resolved path. If the path itself represents
31a transformed file (it has a sourcmap associated with it), then the `loader` should return that
32sourcemap. If not, the path will be treated as an original, untransformed source code.
33
34```js
35// Babel transformed "helloworld.js" into "transformed.js"
36const transformedMap = JSON.stringify({
37 file: 'transformed.js',
38 // 1st column of 2nd line of output file translates into the 1st source
39 // file, line 3, column 2
40 mappings: ';CAEE',
41 sources: ['helloworld.js'],
42 version: 3,
43});
44
45// Uglify minified "transformed.js" into "transformed.min.js"
46const minifiedTransformedMap = JSON.stringify({
47 file: 'transformed.min.js',
48 // 0th column of 1st line of output file translates into the 1st source
49 // file, line 2, column 1.
50 mappings: 'AACC',
51 names: [],
52 sources: ['transformed.js'],
53 version: 3,
54});
55
56const remapped = remapping(
57 minifiedTransformedMap,
58 (file) => {
59
60 // The "transformed.js" file is an transformed file.
61 if (file === 'transformed.js') {
62 return transformedMap;
63 }
64
65 // Loader will be called to load transformedMap's source file pointers as well.
66 console.assert(file === 'helloworld.js');
67 return null;
68 }
69);
70
71console.log(remapped);
72// {
73// file: 'transpiled.min.js',
74// mappings: 'AAEE',
75// sources: ['helloworld.js'],
76// version: 3,
77// };
78```
79
80In this example, `loader` will be called twice:
81
821. `"transformed.js"`, the first source file pointer in the `minifiedTransformedMap`. We return the
83 associated sourcemap for it (its a transformed file, after all) so that sourcemap locations can
84 be traced through it into the source files it represents.
852. `"helloworld.js"`, our original, unmodified source code. This file does not have a sourcemap, so
86 we return `null`.
87
88The `remapped` sourcemap now points from `transformed.min.js` into locations in `helloworld.js`. If
89you were to read the `mappings`, it says "0th column of the first line output line points to the 1st
90column of the 2nd line of the file `helloworld.js`".
91
92### Multiple transformations of a file
93
94As a convenience, if you have multiple single-source transformations of a file, you may pass an
95array of sourcemap files in the order of most-recent transformation sourcemap first. So our above
96example could have been writen as:
97
98```js
99const remapped = remapping(
100 [minifiedTransformedMap, transformedMap],
101 () => null
102);
103
104console.log(remapped);
105// {
106// file: 'transpiled.min.js',
107// mappings: 'AAEE',
108// sources: ['helloworld.js'],
109// version: 3,
110// };
111```
112
113### Options
114
115#### excludeContent
116
117By default, `excludeContent` is `false`. Passing `{ excludeContent: true }`
118will exclude the `sourcesContent` field from the returned sourcemap. This is
119mainly useful when you want to reduce the size out the sourcemap.
120
121#### decodedMappings
122
123By default, `decodedMappings` is `false`. Passing `{ decodedMappings: true }`
124will leave the `mappings` field in a [decoded
125state](https://github.com/rich-harris/sourcemap-codec) instead of encoding
126into a VLQ string.
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