CODEWITHSUNDEEP
javascriptarraysobjectvariablesdata-structures
Suleman Ahmad
Suleman Ahmad

Reputation: 484

Can we use object as a key of an object in Javascript?

I was given a short javascript code in an interview to give the output of that but I was not sure what will be the output of that. He creates a var object and assigns objects as indexes of that object using the array data structure. I did console that code after the interview but still do not understand how it is showing the output.

Here is the code

var a = {};
b = { key: 'b'};
c = { key: 'c'};
a[b] = 123;
a[c] = 456;

console.log(a[b]); //what is the output of this console statement and explain why

Can anyone explain with javascript logic behind the output it shows? Thanks in advance!

Upvotes: 2

Views: 88

Answers (2)

mplungjan
mplungjan

Reputation: 178285

The object used as key's toString is [object Object] and that is what is used each time

var a = {};
b = { key: 'b'};
c = { key: 'c'};
a[b] = 123; // sets a["[object Object]"]
console.log(b,a[b])
a[c] = 456; // ALSO sets a["[object Object]"]
console.log(b,a[b])
console.log(Object.keys(a))
console.log(a[b]);

console.log(a["[object Object]"]);

Upvotes: 4

Nina Scholz
Nina Scholz

Reputation: 386680

You could have a look to the object a, where you see the stringed object (with toString())

[object Object]

as accessor.

Objects can have only strings as properties and with the latest Symbol, it could be this one, too.

var a = {};
b = { key: 'b'};
c = { key: 'c'};
a[b] = 123;
a[c] = 456;

console.log(a[b]); //what is the output of this console statement and explain why
console.log(a);

Upvotes: 1

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