Create array with prototype whose methods implements wrapper over Array prototype

Question

I have array and I want to customize some of his prototype's methods. If i use:

arr.push = function(){
  doSomething()
  Array.prototype.push.call(arguments);
}

I'm creating own property push for arr. But I want to make new array-like object that will have prototype with method push from last example. I've tried to make such thing:

// creating new object which prototype linked to _Array.prototype
var newArr = new (function _Array(){});

// setting up method     
_Array.prototype.push = function(){...}

// copying all data
arr.forEach(function(val, index){ 
  newArr[index] = val;
});
newArr.length = arr.length

//updating original array
arr = Array.prototype.slice.call(newArr);

Yes, after that I will got array-like object, but Array.prototype.slice returns object binded with Array prototype not created by me _Array.prototype.

So can I create array with custom prototype?

friedi · Accepted Answer · 2014-10-29 13:12:36Z

1

You can create your own array this way:

// create own Array object
var _Array = function()  {};

// inherit from Array
_Array.prototype = Object.create(Array.prototype);
// reset constructor
_Array.prototype.constructor = _Array;
// overwrite push method
_Array.prototype.push = function(){
    doSomething()
    Array.prototype.push.apply(this, arguments);
};

You can use it like this:

// create own array
var newArr = new _Array();

// push to array
newArr.push(1, 2, 3);

// create copy
var arr = newArr.slice();

edited Oct 29, 2014 at 13:12

answered Oct 29, 2014 at 13:03

friedi

4,3601 gold badge15 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

wmbtrmb Over a year ago

After execution arr is empty. And when I do arr.push() - calls Array.prototype.push, not _Array.prototype.push. Purpose in ability to create arrays with custom prototype whose methods do something stuff and after it call original method of Array.prototype

HMR Over a year ago

I don't think you can subclass Array: perfectionkills.com/…

HMR · Accepted Answer · 2014-10-29 14:09:00Z

1

I don't think you can subclass Array: http://perfectionkills.com/how-ecmascript-5-still-does-not-allow-to-subclass-an-array/

For example; using _Array:

var arr = new _Array();
arr[10]=22;
console.log(arr.length);//=0

Depending on how much you would like your extended array to behave like an array.

It may be better to just add the function on every array instance in this case and leave the array instance as an array instance instead of creating a type that "inherits" from Array (as it's not possible to inherit from Array):

function createSpecialArray(){
  var ret = new Array(arguments);
  //shadow push
  ret.push = createSpecialArray.push;
  return ret;
};
createSpecialArray.push=function(){
  //do other stuff
  console.log('doing other stuff');
  Array.prototype.push.call(this,arguments);
}

var arr = createSpecialArray(1,2,3);
console.log(arr);
arr[10]=22;
console.log(arr.length);
arr.push(33);
console.log(arr.length);

answered Oct 29, 2014 at 14:09

HMR

39.5k26 gold badges99 silver badges175 bronze badges

2 Comments

wmbtrmb Over a year ago

Thanks for reference. Final purpose was ability to create objects exactly replicating Array behavior in cases of methods that I not changed (up to truthy result for Array.isArray), but, now I see that JS can't do it.

wmbtrmb Over a year ago

On this evidence, I think own properties is the only option.

Collectives™ on Stack Overflow

Create array with prototype whose methods implements wrapper over Array prototype

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related