javascript - I have a question about objects. Can anyone help explain it?

Question

var a={};
var b={key:1};
var c={key:2};
a[b]=3;
a[c] =4;
console.log(a[b]);
I personally think that the content of a[b] should be 3. The above var b and var c are useless, but the actual answer is a[c] is 4, so I can’t understand it. What is the explanation of objects in js? How is this occupied? I hope someone can explain it, thank you very much. . . . . . .

Answer 1

I guess your question is why the value is overwritten, right?
In Javascript, when accesses object properties through [], the expression in square brackets will be evaluated and converted into a string , call its toString method.
So:

var a = {};
b={key:1};
console.log(b.toString()); // [object Object]
a[b]=3;
console.log(typeof Object.keys(a)[0]);    // string, 属性名 b 转换成了字符串.

So b and c are converted into the same string [object Object]. So it will be overwritten if assigned again.

Answer 2

Because b.toString() and c.toString() are both [Object object], so they are the same