Can't force object keys to be integer

Question

const obj = {
15: 100
};
for(let key in obj)
    console.log(key, typeof(key), typeof(+key))

The result is 15 string number. I'm trying to iterate over object values and put some of them into Map object but types compatibility seems unable to achieve. Am I doing something wrong here or object keys are always strings?

Object.keys(obj)

also returns ["15"]

because that is what they actually are. If you want them to be numbers, than map it to a number. `Object.keys(obj).map(k => +k)` — epascarello, Aug 28 '18 at 14:39
Good guess, object keys are strings no matter you denote them with quotes or not. See the question: https://stackoverflow.com/questions/4348478/what-is-the-difference-between-object-keys-with-quotes-and-without-quotes — vahdet, Aug 28 '18 at 14:39
Even an array's keys are, internally, strings: `console.log(Object.keys([1,2,3,4]));` — Cerbrus, Aug 28 '18 at 14:43

score 7 · Accepted Answer · answered Aug 28 '18 at 14:42

Object keys are always strings. You can see more about it here:

Property names must be strings. This means that non-string objects cannot be used as keys in the object. Any non-string object, including a number, is typecasted into a string via the toString method.

For you to be able to achieve what you want you will need to cast the keys back to integers.

Can't force object keys to be integer

1 Answers1