throttle.js

var debounce = require('./debounce'),
    isObject = require('../lang/isObject');

/** Used as the `TypeError` message for "Functions" methods. */
var FUNC_ERROR_TEXT = 'Expected a function';

/** Used as an internal `_.debounce` options object by `_.throttle`. */
var debounceOptions = {
  'leading': false,
  'maxWait': 0,
  'trailing': false
};

/**
 * Creates a throttled function that only invokes `func` at most once per
 * every `wait` milliseconds. The throttled function comes with a `cancel`
 * method to cancel delayed invocations. Provide an options object to indicate
 * that `func` should be invoked on the leading and/or trailing edge of the
 * `wait` timeout. Subsequent calls to the throttled function return the
 * result of the last `func` call.
 *
 * **Note:** If `leading` and `trailing` options are `true`, `func` is invoked
 * on the trailing edge of the timeout only if the the throttled function is
 * invoked more than once during the `wait` timeout.
 *
 * See [David Corbacho's article](http://drupalmotion.com/article/debounce-and-throttle-visual-explanation)
 * for details over the differences between `_.throttle` and `_.debounce`.
 *
 * @static
 * @memberOf _
 * @category Function
 * @param {Function} func The function to throttle.
 * @param {number} [wait=0] The number of milliseconds to throttle invocations to.
 * @param {Object} [options] The options object.
 * @param {boolean} [options.leading=true] Specify invoking on the leading
 *  edge of the timeout.
 * @param {boolean} [options.trailing=true] Specify invoking on the trailing
 *  edge of the timeout.
 * @returns {Function} Returns the new throttled function.
 * @example
 *
 * // avoid excessively updating the position while scrolling
 * jQuery(window).on('scroll', _.throttle(updatePosition, 100));
 *
 * // invoke `renewToken` when the click event is fired, but not more than once every 5 minutes
 * jQuery('.interactive').on('click', _.throttle(renewToken, 300000, {
 *   'trailing': false
 * }));
 *
 * // cancel a trailing throttled call
 * jQuery(window).on('popstate', throttled.cancel);
 */
function throttle(func, wait, options) {
  var leading = true,
      trailing = true;

  if (typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  if (options === false) {
    leading = false;
  } else if (isObject(options)) {
    leading = 'leading' in options ? !!options.leading : leading;
    trailing = 'trailing' in options ? !!options.trailing : trailing;
  }
  debounceOptions.leading = leading;
  debounceOptions.maxWait = +wait;
  debounceOptions.trailing = trailing;
  return debounce(func, wait, debounceOptions);
}

module.exports = throttle;