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 — ShadowRanger
– ShadowRanger, Commented Jan 20, 2022 at 0:24

UtkarshPramodGupta · Accepted Answer · 2022-01-20 00:26:56Z

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');

Matthieu Riegler · Accepted Answer · 2022-01-20 00:30:02Z

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, 2022 at 0:30

Matthieu Riegler

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3 Comments

David542 Over a year ago

@mathieu -- I see, I think that's the closest approach. But so in modern js there is no way to override the bare == check?

Matthieu Riegler Over a year ago

Nope, not at the moment.

UtkarshPramodGupta Over a year ago

@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.

Thenlie · Accepted Answer · 2022-01-20 00:25:04Z

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, 2022 at 0:25

Thenlie

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2 Comments

David542 Over a year ago

I see, so there's no way to override the == operator, like you could do in python with __eq__ ?

Matthieu Riegler Over a year ago

No way no, but you could do p1.valueOf() == p2.valueOf()

Luiz Calaça · Accepted Answer · 2022-01-20 00:32:42Z

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

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