Javascript object computed property [duplicate]

Object keys may only be strings. When you put an object in a computed property, it will be stringified to [object Object], so a[b] is the same as a[c]: a['[object Object]'].

let a = {};

let b = {
    value: 'b'
};

let c = {
    value: 'c'
};

a[b]=123;
a[c]=456;

console.log(a);

So, the final assignment of 456 to the [object Object] key overwrites the prior assignment of 123 (and the resulting object only has that one key).

If you want to safely use objects as "keys", use a Map instead, whose keys can be of any type, not just strings:

const a = new Map();

let b = {
    value: 'b'
};

let c = {
    value: 'c'
};

a.set(b, 123);
a.set(c, 456);
console.log(a.get(b));
console.log(a.get(c));

Quite easy:

When you do

a[b]=123;
a[c]=456;

you set an object as a propery name of a.

The thing is, a property name is a string, so, toString() is called on b and c (which are objects), and that makes the same value. Do you get it?

let a = {};

let b = {
    value: 'b'
};

let c = {
    value: 'c'
};

a[b]=123;
a[c]=456;

console.log(a[b], a[c]); // ==> 456 456
console.log(a);

In a[b] = //... expression, b gets coerced to string - and the result of that conversion is a string "[object Object]". And it's the same value for c.

let a = {};

let b = {
    value: 'b'
};

let c = {
    value: 'c'
};

a[b]=123;
a[c]=456;

console.log(b.toString());
console.log(c.toString());

console.log(a);

Because Object's key can be string and you are trying to assign a object as the key, js typecasts the object to string and the key becomes [object Object] for both the objects. That is why the value is updated against the same key.