Polyfills for Jade

[].filter || (Array.prototype.filter = // Use the native array filter method, if available.
  function(a, //a function to test each value of the array against. Truthy values will be put into the new array and falsy values will be excluded from the new array
    b, // placeholder
    c, // placeholder
    d, // placeholder
    e // placeholder
  ) {
      c = this; // cache the array
      d = []; // array to hold the new values which match the expression
      for (e in c) // for each value in the array,
        ~~e + '' == e && e >= 0 && // coerce the array position and if valid,
        a.call(b, c[e], +e, c) && // pass the current value into the expression and if truthy,
        d.push(c[e]); // add it to the new array

      return d // give back the new array
  })


/**
 * Polyfill for Object.keys
 *
 * @see: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Object/keys
 */
if (!Object.keys) {
  Object.keys = (function () {
    var hasOwnProperty = Object.prototype.hasOwnProperty,
        hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'),
        dontEnums = [
          'toString',
          'toLocaleString',
          'valueOf',
          'hasOwnProperty',
          'isPrototypeOf',
          'propertyIsEnumerable',
          'constructor'
        ],
        dontEnumsLength = dontEnums.length;

    return function (obj) {
      if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object');

      var result = [];

      for (var prop in obj) {
        if (hasOwnProperty.call(obj, prop)) result.push(prop);
      }

      if (hasDontEnumBug) {
        for (var i=0; i < dontEnumsLength; i++) {
          if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i]);
        }
      }
      return result;
    }
  })()
};


if (!Array.isArray) {
  Array.isArray = function(arg) {
    return Object.prototype.toString.call(arg) === '[object Array]';
  };
}


// Array.map polyfill
if (Array.prototype.map === undefined) {
  Array.prototype.map = function(fn) {
    var rv = [];

    for(var i=0, l=this.length; i<l; i++)
      rv.push(fn(this[i]));

    return rv;
  };
}