1
(function () {
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  if (typeof window.Element === "undefined" ||
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      "classList" in document.documentElement) {
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    return;
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  }
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  var prototype = Array.prototype,
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      push = prototype.push,
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      splice = prototype.splice,
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      join = prototype.join;
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  function DOMTokenList(el) {
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    this.el = el;
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    // The className needs to be trimmed and split on whitespace
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    // to retrieve a list of classes.
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    var classes = el.className.replace(/^\s+|\s+$/g, '').split(/\s+/);
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    for (var i = 0; i < classes.length; i++) {
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      push.call(this, classes[i]);
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    }
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  }
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  DOMTokenList.prototype = {
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    add: function (token) {
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      if (this.contains(token)) return;
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      push.call(this, token);
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      this.el.className = this.toString();
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    },
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    contains: function (token) {
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      return this.el.className.indexOf(token) != -1;
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    },
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    item: function (index) {
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      return this[index] || null;
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    },
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    remove: function (token) {
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      if (!this.contains(token)) return;
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      for (var i = 0; i < this.length; i++) {
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        if (this[i] == token) break;
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      }
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      splice.call(this, i, 1);
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      this.el.className = this.toString();
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    },
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    toString: function () {
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      return join.call(this, ' ');
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    },
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    toggle: function (token) {
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      if (!this.contains(token)) {
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        this.add(token);
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      } else {
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        this.remove(token);
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      }
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      return this.contains(token);
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    }
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  };
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  window.DOMTokenList = DOMTokenList;
57

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  function defineElementGetter(obj, prop, getter) {
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    if (Object.defineProperty) {
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      Object.defineProperty(obj, prop, {
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        get: getter
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      });
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    } else {
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      obj.__defineGetter__(prop, getter);
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    }
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  }
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  defineElementGetter(HTMLElement.prototype, 'classList', function () {
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    return new DOMTokenList(this);
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  });
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})();
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