echo/dist/echo.js

/*! Echo v1.4.0 | (c) 2014 @toddmotto | MIT license | github.com/toddmotto/echo */
(function (name, context, definition) {

  'use strict';

  if (typeof define === 'function' && define.amd) {
    define(definition);
  }
  else if (typeof module !== 'undefined' && module.exports) {
    module.exports = definition();
  }
  else {
    context[name] = definition();
  }
})('Echo', this, function() {

  'use strict';

  function Echo() {

    var store = [], offset, throttle, poll;

    var _inView = function (el) {
      var coords = el.getBoundingClientRect();
      return ((coords.top >= 0 && coords.left >= 0 && coords.top) <= (window.innerHeight || document.documentElement.clientHeight) + parseInt(offset));
    };

    var _pollImages = function () {
      for (var i = store.length; i--;) {
        var self = store[i];
        if (_inView(self)) {
          self.src = self.getAttribute('data-echo');
          store.splice(i, 1);
        }
      }
    };

    var _throttle = function () {
      clearTimeout(poll);
      poll = setTimeout(_pollImages, throttle);
    };

    var init = function (obj) {
      var nodes = document.querySelectorAll('[data-echo]');
      var opts = obj || {};
      offset = opts.offset || 0;
      throttle = opts.throttle || 250;

      for (var i = 0; i < nodes.length; i++) {
        store.push(nodes[i]);
      }

      _throttle();

      if (document.addEventListener) {
        window.addEventListener('scroll', _throttle, false);
      } else {
        window.attachEvent('onscroll', _throttle);
      }
    };

    return {
      init: init,
      render: _throttle
    };

  }

  return Echo;

});