How can i effectively prototype Array or from Array to reuse code?

Question

I built a parser and I would like to 'extend' the Array class in order to use the same functions but have not been successful with:

Array.prototype = new Parser()

I would like to create a function that would reuse the shift from the array without me having to add:

function() { return this.list.shift() }

Also I've been having some problems with the this identity so:

How can i effectively prototype Array or from Array to reuse code ?

function Parser() {
  this.get_info_colors = function() {
    return {
      'id': self.shift(),
      'name': self.shift(),
      'colors': self.get_colors()
    }
  }
  this.get_info_grad = function() {
    return {
      'id': self.shift(),
      'name': (self.shift() + '_grad'),
      'grad': self.shift()
    }
  }
  this.get_colors = function() {
    this.shift();
    var result = [],
        element;
    while(element != ']') {
      element = this.shift();
      result.push();
    }
    return element;
  }
  this.builder = function(factory) {
    this.shift();
    var result = [],
        element;
    while(element != ']') {
      result.push(factory());
    }
    return result;
  }
  this.color_builder = function() {
    return this.builder(this.get_info_colors);
  }
  this.grad_builder = function() {
    return this.builder(this.get_info_grad);
  }
}

Thanks in advance.

thefourtheye · Accepted Answer · 2014-04-14 14:18:32Z

1

To extend Array, you need to extend its prototype, like this

function CustomArray() {}
CustomArray.prototype = Object.create(Array.prototype);
CustomArray.constructor = CustomArray;

And then you can add all your custom methods on the CustomArray's prototype, like this

CustomArray.prototype.newMethod = function() {...}

answered Apr 14, 2014 at 14:18

thefourtheye

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1 Comment

Felix Kling Over a year ago

While this adds the array methods to the custom object, it doesn't make it behave like an array. E.g. using property assignment like obj[3] = 42; won't increase the length of the "custom array". Just wanted to make that clear.

Fuzzyma · Accepted Answer · 2014-04-14 14:20:27Z

1

I use Array.prototype.parser = function(){ // your parser }

answered Apr 14, 2014 at 14:20

Fuzzyma

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Comments

Community · Accepted Answer · 2017-05-23 10:25:23Z

1

First of all, see this post:

Why is extending native objects a bad practice?

Second, do you want to extend Parser to derive methods of Array or vice versa? Basically it would be quite okay to have Parser derive methods from Array, but then your prototype assignment is wrong.

Parser.prototype = [];

Did you try it that way.

Regarding your issues with this the posted code isn't complete, is it?

EDIT : Some example:

function Parser() { this.__a = 1; }
Parser.prototype = [];
var a = new Parser;
a.length
// gives 0
a.push( 2 );
// gives 1
a.length
// gives 1
a.__a
// gives 1

EDIT 2 : Example for using constructor as given in comments:

function Parser() { 
  var args = [].slice.call( arguments );
  args.unshift( 0 ); 
  args.unshift( 0 ); 
  [].splice.apply( this, args ); 
}

Parser.prototype = [];

var c = new Parser( 1, 2, 3 )
c.length
// gives 3

edited May 23, 2017 at 10:25

CommunityBot

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answered Apr 14, 2014 at 14:24

Thomas Urban

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8 Comments

user1634074 Over a year ago

Its not they started when I did Parser.prototype = [] the this turned into window.

Thomas Urban Over a year ago

Using this is very special ... this is a special local variable in context of your function, only, to be declared on invoking.

user1634074 Over a year ago

If I do Parser.prototype. Then how can I turn [1,2,3,4] into new Parser(1,2,3,4).

Thomas Urban Over a year ago

Your "constructor" might use arguments to push all its elements into array using push() ... ain't performant, but sufficient for this sort of syntactical sugar.

Thomas Urban Over a year ago

Tried the second example above in Google Chrome before providing here. Tried it with NodeJS right this moment again. It was working in both situations and this time I was able to append c.shift(); four times giving me 1, 2, 3 and undefined ... so it is working. What context are you working in? What is your engine/browser for testing this?

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