function my_func(item) {

  if (item == ) {

    console.log('t');

    return true;

  }

  console.log('f');

  return false;

}

// init an array

l = [,,,,]

// print: f,t,f,f,f

// return:[false, true, false, false, false]

l.map(my_func)

// print: f,t,f,f,f

// return: 1

l.filter(my_func)

// print: f,t

// return: true

l.some(my_func)

// print: f

// return: false

l.every(my_func)

// print: f,t,f,f,f

//return: undefined

l.forEach(my_func)

Array.prototype.map = function(fun /*, thisp*/)

{

  var len = this.length;

  if (typeof fun != "function")

    throw new TypeError();

  var res = new Array(len);

  var thisp = arguments[];

  for (var i = ; i < len; i++)

  {

    if (i in this)

      res[i] = fun.call(thisp, this[i], i, this);

  }

  return res;

};

Array.prototype.filter = function(fun /*, thisp*/)

{

  var len = this.length;

  if (typeof fun != "function")

    throw new TypeError();

  var res = new Array();

  var thisp = arguments[];

  for (var i = ; i < len; i++)

  {

    if (i in this)

    {

      var val = this[i]; // in case fun mutates this

      if (fun.call(thisp, val, i, this))

        res.push(val);

    }

  }

  return res;

};

Array.prototype.some = function(fun /*, thisp*/)

{

  var len = this.length;

  if (typeof fun != "function")

    throw new TypeError();

  var thisp = arguments[];

  for (var i = ; i < len; i++)

  {

    if (i in this && fun.call(thisp, this[i], i, this))

      return true;

  }

  return false;

};

Array.prototype.every = function(fun /*, thisp*/)

{

  var len = this.length;

  if (typeof fun != "function")

    throw new TypeError();

  var thisp = arguments[];

  for (var i = ; i < len; i++)

  {

    if (i in this && !fun.call(thisp, this[i], i, this))

    return false;

  }

  return true;

};

Array.prototype.forEach = function(fun /*, thisp*/)

{

  var len = this.length;

  if (typeof fun != "function")

    throw new TypeError();

  var thisp = arguments[];

  for (var i = ; i < len; i++)

  {

    if (i in this)

      fun.call(thisp, this[i], i, this);

  }

};