/functions/var/is_array.js

function is_array(mixed_var) {
  //  discuss at: http://phpjs.org/functions/is_array/
  // original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // improved by: Legaev Andrey
  // improved by: Onno Marsman
  // improved by: Brett Zamir (http://brett-zamir.me)
  // improved by: Nathan Sepulveda
  // improved by: Brett Zamir (http://brett-zamir.me)
  // bugfixed by: Cord
  // bugfixed by: Manish
  // bugfixed by: Brett Zamir (http://brett-zamir.me)
  //        note: In php.js, javascript objects are like php associative arrays, thus JavaScript objects will also
  //        note: return true in this function (except for objects which inherit properties, being thus used as objects),
  //        note: unless you do ini_set('phpjs.objectsAsArrays', 0), in which case only genuine JavaScript arrays
  //        note: will return true
  //   example 1: is_array(['Kevin', 'van', 'Zonneveld']);
  //   returns 1: true
  //   example 2: is_array('Kevin van Zonneveld');
  //   returns 2: false
  //   example 3: is_array({0: 'Kevin', 1: 'van', 2: 'Zonneveld'});
  //   returns 3: true
  //   example 4: is_array(function tmp_a(){this.name = 'Kevin'});
  //   returns 4: false

  var ini,
    _getFuncName = function(fn) {
      var name = (/\W*function\s+([\w\$]+)\s*\(/)
        .exec(fn);
      if (!name) {
        return '(Anonymous)';
      }
      return name[1];
    };
  _isArray = function(mixed_var) {
    // return Object.prototype.toString.call(mixed_var) === '[object Array]';
    // The above works, but let's do the even more stringent approach: (since Object.prototype.toString could be overridden)
    // Null, Not an object, no length property so couldn't be an Array (or String)
    if (!mixed_var || typeof mixed_var !== 'object' || typeof mixed_var.length !== 'number') {
      return false;
    }
    var len = mixed_var.length;
    mixed_var[mixed_var.length] = 'bogus';
    // The only way I can think of to get around this (or where there would be trouble) would be to have an object defined
    // with a custom "length" getter which changed behavior on each call (or a setter to mess up the following below) or a custom
    // setter for numeric properties, but even that would need to listen for specific indexes; but there should be no false negatives
    // and such a false positive would need to rely on later JavaScript innovations like __defineSetter__
    if (len !== mixed_var.length) {
      // We know it's an array since length auto-changed with the addition of a
      // numeric property at its length end, so safely get rid of our bogus element
      mixed_var.length -= 1;
      return true;
    }
    // Get rid of the property we added onto a non-array object; only possible
    // side-effect is if the user adds back the property later, it will iterate
    // this property in the older order placement in IE (an order which should not
    // be depended on anyways)
    delete mixed_var[mixed_var.length];
    return false;
  };

  if (!mixed_var || typeof mixed_var !== 'object') {
    return false;
  }

  // BEGIN REDUNDANT
  this.php_js = this.php_js || {};
  this.php_js.ini = this.php_js.ini || {};
  // END REDUNDANT

  ini = this.php_js.ini['phpjs.objectsAsArrays'];

  return _isArray(mixed_var) ||
    // Allow returning true unless user has called
    // ini_set('phpjs.objectsAsArrays', 0) to disallow objects as arrays
    ((!ini || (// if it's not set to 0 and it's not 'off', check for objects as arrays
      (parseInt(ini.local_value, 10) !== 0 && (!ini.local_value.toLowerCase || ini.local_value.toLowerCase() !==
        'off')))) && (
      Object.prototype.toString.call(mixed_var) === '[object Object]' && _getFuncName(mixed_var.constructor) ===
      'Object' // Most likely a literal and intended as assoc. array
    ));
}