我们可以使用 object 作为 Javascript 中的一个 object 的密钥吗？

Question

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!

Answer 1

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]"]);

Answer 2

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);