What is the type of object keys in JavaScript?

In JavaScript, an object treats each key as a string whether it's a number value, boolean value or any other primitive value.

HelloWorld.js

var obj = {"id" : 123, 1 : "2", 2 : "3", 3 : "5", true : true};

for(var key in obj){
  console.log(key + " : " + typeof key)
}

Output

1 : string

2 : string

3 : string

id : string
true : string

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