1var debounce = require('./debounce'),
2    isObject = require('./isObject');
3
4/** Error message constants. */
5var FUNC_ERROR_TEXT = 'Expected a function';
6
7/**
8 * Creates a throttled function that only invokes `func` at most once per
9 * every `wait` milliseconds. The throttled function comes with a `cancel`
10 * method to cancel delayed `func` invocations and a `flush` method to
11 * immediately invoke them. Provide `options` to indicate whether `func`
12 * should be invoked on the leading and/or trailing edge of the `wait`
13 * timeout. The `func` is invoked with the last arguments provided to the
14 * throttled function. Subsequent calls to the throttled function return the
15 * result of the last `func` invocation.
16 *
17 * **Note:** If `leading` and `trailing` options are `true`, `func` is
18 * invoked on the trailing edge of the timeout only if the throttled function
19 * is invoked more than once during the `wait` timeout.
20 *
21 * If `wait` is `0` and `leading` is `false`, `func` invocation is deferred
22 * until to the next tick, similar to `setTimeout` with a timeout of `0`.
23 *
24 * See [David Corbacho's article](https://css-tricks.com/debouncing-throttling-explained-examples/)
25 * for details over the differences between `_.throttle` and `_.debounce`.
26 *
27 * @static
28 * @memberOf _
29 * @since 0.1.0
30 * @category Function
31 * @param {Function} func The function to throttle.
32 * @param {number} [wait=0] The number of milliseconds to throttle invocations to.
33 * @param {Object} [options={}] The options object.
34 * @param {boolean} [options.leading=true]
35 *  Specify invoking on the leading edge of the timeout.
36 * @param {boolean} [options.trailing=true]
37 *  Specify invoking on the trailing edge of the timeout.
38 * @returns {Function} Returns the new throttled function.
39 * @example
40 *
41 * // Avoid excessively updating the position while scrolling.
42 * jQuery(window).on('scroll', _.throttle(updatePosition, 100));
43 *
44 * // Invoke `renewToken` when the click event is fired, but not more than once every 5 minutes.
45 * var throttled = _.throttle(renewToken, 300000, { 'trailing': false });
46 * jQuery(element).on('click', throttled);
47 *
48 * // Cancel the trailing throttled invocation.
49 * jQuery(window).on('popstate', throttled.cancel);
50 */
51function throttle(func, wait, options) {
52  var leading = true,
53      trailing = true;
54
55  if (typeof func != 'function') {
56    throw new TypeError(FUNC_ERROR_TEXT);
57  }
58  if (isObject(options)) {
59    leading = 'leading' in options ? !!options.leading : leading;
60    trailing = 'trailing' in options ? !!options.trailing : trailing;
61  }
62  return debounce(func, wait, {
63    'leading': leading,
64    'maxWait': wait,
65    'trailing': trailing
66  });
67}
68
69module.exports = throttle;
70