How to determine equality for two ES6 class instances?

Question

How to determine equality between two ES6 class object instances? For example:

class Rectangle {
  constructor(height, width) {    
    this.height = height;
    this.width = width;
  }
}

(new Rectangle(1, 1)) === (new Rectangle(1, 1))
(new Rectangle(3, 0)) === (new Rectangle(9, 3))

The last two statements return false, but I want it to return true, to compare the instance properties, instead of the object references.

There is no operator overloading in JavaScript, and objects are compared by reference, not by property values. You'll need to define your own function to compare them. — Heretic Monkey, Jan 11 '19 at 18:05
Well.... I want a jaguar, doesn't mean it will happen. You are doing a comparison between two memory references that are not pointing to the same address, this returning true would be wrong. You need to implement a method on the prototype of the constructor function that will recognize it's children by some means, the `===` is not what will get you the results sadly. — Dellirium, Jan 11 '19 at 18:05
The best method would probably be to create an `.equals()` method — Sebastian Speitel, Jan 11 '19 at 18:05

score 4 · Accepted Answer · edited Jan 11 '19 at 18:27

4

Add a method to the Rectangle class:

class Rectangle {
  constructor(height, width) {    
    this.height = height;
    this.width = width;
  }
  equals(rect) {
    return this.width == rect.width && this.height == rect.height;
  }
}

edited Jan 11 '19 at 18:27

Bergi

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answered Jan 11 '19 at 18:10

Sam Alexander

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How to determine equality for two ES6 class instances?

1 Answers1