decca/lib/debounce.js

Render interfaces using pure functions and virtual DOM, kinda

"use strict";

/**
 * Module dependencies.
 */

var now = Date.now || function () {
  return new Date().getTime();
};

/**
 * Returns a function, that, as long as it continues to be invoked, will not
 * be triggered. The function will be called after it stops being called for
 * N milliseconds. If `immediate` is passed, trigger the function on the
 * leading edge, instead of the trailing.
 *
 * @source underscore.js
 * @see http://unscriptable.com/2009/03/20/debouncing-javascript-methods/
 * @param {Function} function to wrap
 * @param {Number} timeout in ms (`100`)
 * @param {Boolean} whether to execute at the beginning (`false`)
 * @api public
 */

module.exports = function debounce(func, wait, immediate) {
  var timeout, args, context, timestamp, result;
  if (wait == null) wait = 100;

  function later() {
    var last = now() - timestamp;

    if (last < wait && last > 0) {
      timeout = setTimeout(later, wait - last);
    } else {
      timeout = null;
      if (!immediate) {
        result = func.apply(context, args);
        if (!timeout) context = args = null;
      }
    }
  }

  function debounced() {
    debounced.calls++;
    context = this;
    args = arguments;
    timestamp = now();
    var callNow = immediate && !timeout;
    if (!timeout) timeout = setTimeout(later, wait);
    if (callNow) {
      result = func.apply(context, args);
      context = args = null;
    }

    return result;
  }

  debounced.calls = 0;

  debounced.cancel = function () {
    context = args = null;
    if (timeout) {
      clearTimeout(timeout);
      timeout = null;
    }
    timestamp = now();
  };

  return debounced;
};