1 | import debounce from './debounce.js';
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2 | import isObject from './isObject.js';
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3 |
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4 | /** Error message constants. */
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5 | var FUNC_ERROR_TEXT = 'Expected a function';
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6 |
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7 | /**
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8 | * Creates a throttled function that only invokes `func` at most once per
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9 | * every `wait` milliseconds. The throttled function comes with a `cancel`
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10 | * method to cancel delayed `func` invocations and a `flush` method to
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11 | * immediately invoke them. Provide `options` to indicate whether `func`
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12 | * should be invoked on the leading and/or trailing edge of the `wait`
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13 | * timeout. The `func` is invoked with the last arguments provided to the
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14 | * throttled function. Subsequent calls to the throttled function return the
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15 | * result of the last `func` invocation.
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16 | *
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17 | * **Note:** If `leading` and `trailing` options are `true`, `func` is
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18 | * invoked on the trailing edge of the timeout only if the throttled function
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19 | * is invoked more than once during the `wait` timeout.
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20 | *
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21 | * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred
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22 | * until to the next tick, similar to `setTimeout` with a timeout of `0`.
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23 | *
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24 | * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/)
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25 | * for details over the differences between `_.throttle` and `_.debounce`.
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26 | *
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27 | * @static
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28 | * @memberOf _
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29 | * @since 0.1.0
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30 | * @category Function
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31 | * @param {Function} func The function to throttle.
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32 | * @param {number} [wait=0] The number of milliseconds to throttle invocations to.
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33 | * @param {Object} [options={}] The options object.
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34 | * @param {boolean} [options.leading=true]
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35 | * Specify invoking on the leading edge of the timeout.
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36 | * @param {boolean} [options.trailing=true]
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37 | * Specify invoking on the trailing edge of the timeout.
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38 | * @returns {Function} Returns the new throttled function.
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39 | * @example
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40 | *
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41 | * // Avoid excessively updating the position while scrolling.
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42 | * jQuery(window).on('scroll', _.throttle(updatePosition, 100));
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43 | *
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44 | * // Invoke `renewToken` when the click event is fired, but not more than once every 5 minutes.
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45 | * var throttled = _.throttle(renewToken, 300000, { 'trailing': false });
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46 | * jQuery(element).on('click', throttled);
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47 | *
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48 | * // Cancel the trailing throttled invocation.
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49 | * jQuery(window).on('popstate', throttled.cancel);
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50 | */
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51 | function throttle(func, wait, options) {
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52 | var leading = true,
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53 | trailing = true;
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54 |
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55 | if (typeof func != 'function') {
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56 | throw new TypeError(FUNC_ERROR_TEXT);
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57 | }
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58 | if (isObject(options)) {
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59 | leading = 'leading' in options ? !!options.leading : leading;
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60 | trailing = 'trailing' in options ? !!options.trailing : trailing;
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61 | }
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62 | return debounce(func, wait, {
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63 | 'leading': leading,
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64 | 'maxWait': wait,
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65 | 'trailing': trailing
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66 | });
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67 | }
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68 |
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69 | export default throttle;
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