Javascript: make an object inherit array methods

Question

var RPNCalculator = function() {
    this.stack = [];
    this.total = 0;
    this.value = function() {
        return this.total;
    }
    this.push = function(val) {
       this.stack.push(val);
    }
    this.pop = function() {
        this.stack.pop();
    }
    this.process = function() {
        this.val1 = this.stack.pop();
        this.val2 = this.stack.pop();
        this.total = 0;
    }
    this.plus = function() {
        this.process();
        this.total = this.val1 + this.val2;
        this.stack.push(this.total);  
    }
    this.minus = function() {
        this.process();
        this.total = this.val2 - this.val1;
        this.stack.push(this.total);  
    }
}

How can I make the RPNCalculator object inherit array methods, without creating push and pop methods myself? For example, if I do the following

rpnCalculator = new RPNCalculator();
rpnCalculator.push(2);

it will add the number 2 to the stack array

Your best bet would be not to use a .stack property and instead make RPNCalculator instance array-like. — Bergi
– Bergi, Commented Jun 30, 2015 at 0:50

Jason Cust · Accepted Answer · 2015-06-30 00:58:24Z

1

If you want all of the methods provided by Array maybe start with inheriting the prototype from Array using Object.create and then adding your custom functions to the new constructor prototype.

var Foo = function () {};
Foo.prototype = Object.create(Array.prototype);
Foo.prototype.process = function process() {
  // `this` is the array
  // Do some logic...

  // returning `this` to show it is the array
  return this;
}

var foo = new Foo();
foo.push(3);
foo.push(2);
foo.push(1);

document.write(
  '<h3>foo</h3>' + 
  '<pre>' + JSON.stringify(foo, null, 4) + '</pre>' +
  '<h3>foo.process()</h3>' +
  '<pre>' + JSON.stringify(foo.process(), null, 4) + '</pre>'
);

edited Jun 30, 2015 at 0:58

answered Jun 30, 2015 at 0:47

Jason Cust

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1 Comment

Mark Pytel Over a year ago

Thanks for the suggestions! I will do my best to learn from these.

TheDude · Accepted Answer · 2015-06-30 00:32:34Z

1

You could do:

this.push = this.stack.push.bind(this.stack); this.pop = this.stack.pop.bind(this.stack);

That would just use stack's methods instead of defining your own.

answered Jun 30, 2015 at 0:32

TheDude

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4 Comments

Mark Pytel Over a year ago

thank you. i was under the impression that there was a way to define the object using prototypes, so that it could inherit all the array methods. something involving underscoreunderscorePROTOunderscoreunderscore. i am very new to this so i apologize if i am not making much sense.

Jan Over a year ago

Check out Jason's answer

TheDude Over a year ago

The problem you defined does not need prototypical inheritance to solve it though. Since you only need two methods, why bring in everything else Array.protype has?

Mark Pytel Over a year ago

You are correct, I do not need to inherit all the Array properties. Your answer was very helpful, and it's a technique I was not aware of. I just figured while I am here I could get more information relevant to the topic.

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