annotate core/misc/debounce.es6.js @ 19:fa3358dc1485 tip

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/**
 * @file
 * Adapted from underscore.js with the addition Drupal namespace.
 */

/**
 * Limits the invocations of a function in a given time frame.
 *
 * The debounce function wrapper should be used sparingly. One clear use case
 * is limiting the invocation of a callback attached to the window resize event.
 *
 * Before using the debounce function wrapper, consider first whether the
 * callback could be attached to an event that fires less frequently or if the
 * function can be written in such a way that it is only invoked under specific
 * conditions.
 *
 * @param {function} func
 *   The function to be invoked.
 * @param {number} wait
 *   The time period within which the callback function should only be
 *   invoked once. For example if the wait period is 250ms, then the callback
 *   will only be called at most 4 times per second.
 * @param {bool} immediate
 *   Whether we wait at the beginning or end to execute the function.
 *
 * @return {function}
 *   The debounced function.
 */
Drupal.debounce = function(func, wait, immediate) {
  let timeout;
  let result;
  return function(...args) {
    const context = this;
    const later = function() {
      timeout = null;
      if (!immediate) {
        result = func.apply(context, args);
      }
    };
    const callNow = immediate && !timeout;
    clearTimeout(timeout);
    timeout = setTimeout(later, wait);
    if (callNow) {
      result = func.apply(context, args);
    }
    return result;
  };
};