Doing an operator (==) equality check in js

Question

I have the following class:

class Coord {
    constructor(x, y) {
        this.x = x;
        this.y = y
    }
    equals(b) { // how to add this method?
        return true;
    }
}

let p1 = new Coord(1,2);
let p2 = new Coord(1,2);
console.assert(p1 == p2, 'points are not equal');

Is there a method I can add into the class such that p1 == p2 in the above? I'd like to do it within the class and not something like a JSONStringify approach.

The equivalent in python I would do would be:

class Coord:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __eq__(self, o):
        return (self.x == o.x) and (self.y == o.y)

p1 = Coord(1,2);
p2 = Coord(1,2);
print (p1==p2)
# True

Does this answer your question? [Override the Equivalence Comparison in Javascript](https://stackoverflow.com/questions/10539938/override-the-equivalence-comparison-in-javascript) — ShadowRanger, Jan 20 '22 at 00:24

score 2 · Answer 1 · answered Jan 20 '22 at 00:26

There you go :)

class Coord {
    constructor(x, y) {
        this.x = x;
        this.y = y
    }
    
    print() {
        console.log('(' + `%c${this.x}` + ', ' + `%c${this.y}` + '%c)', "color:red", "color: blue", "color: black");
    }
    
    equals(b) {
        return (this.x===b.x && this.y===b.y);
    }
}

let p1 = new Coord(1,2);
let p2 = new Coord(1,2);
let p3 = new Coord(1,3);
let p4 = new Coord(4,2);

console.assert(p1.equals(p2), 'p1 and p2 are not equal');
console.assert(p1.equals(p3), 'p1 and p3 are not are not equal');
console.assert(p1.equals(p4), 'p1 and p4 points are not equal');

score 1 · Answer 2 · answered Jan 20 '22 at 00:25

1

If you are trying to compare two instances of the Coord class you will not be able to do that within the class itself. How you have it set up seems like a decent approach. You could also compare the coordinate values before creating the class.

answered Jan 20 '22 at 00:25

Thenlie

674
8
15

I see, so there's no way to override the `==` operator, like you could do in python with [`__eq__`](https://docs.python.org/3/reference/datamodel.html#object.__eq__) ? – David542 Jan 20 '22 at 00:26
1

No way no, but you could do `p1.valueOf() == p2.valueOf()` – Matthieu Riegler Jan 20 '22 at 00:28

score 1 · Accepted Answer · answered Jan 20 '22 at 00:30

1

An alternative

class Coord {
    constructor(x, y) {
        this.x = x;
        this.y = y
    }

    valueOf(b) { 
        return `${x},${y}`
    }
}

let p1 = new Coord(1,2);
let p2 = new Coord(1,2);
console.assert(p1.valueOf() == p2.valueOf(), 'points are not equal');

answered Jan 20 '22 at 00:30

Matthieu Riegler

31,918
20
95
134

@mathieu -- I see, I think that's the closest approach. But so in modern js there is no way to override the bare `==` check? – David542 Jan 20 '22 at 00:31
Nope, not at the moment. – Matthieu Riegler Jan 20 '22 at 00:31
@MatthieuRiegler -- It's kinda an anti-pattern to override natively available methods like `valueOf`. It can lead to bugs in code. The better approach would be to have a non-native method for the same. – UtkarshPramodGupta Jan 20 '22 at 00:54

score 0 · Answer 4 · answered Jan 20 '22 at 00:32

0

One option is using lodash (https://lodash.com/docs/4.17.15#isEqual)

Example from lodash documentation:

var object = { 'a': 1 };
var other = { 'a': 1 };
 
_.isEqual(object, other);
// => true
 
object === other;
// => false

answered Jan 20 '22 at 00:32

Luiz Calaça

61
1
7

Doing an operator (==) equality check in js

4 Answers4