Lessons · JavaScript · object keys are text

Object keys are strings

Whatever you use as a key on a plain object becomes a string. Numbers work by accident; objects collapse to '[object Object]'.

Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.

What it is for

Keying by user objects or coordinates on a plain object silently merges everything into one key. Map keeps real keys.

How to think about it

Are my keys strings, or something else? Strings and small integers as keys: object is fine. Anything else, or when you need insertion order and size: use Map.

Worked example

const o = {}; o[1] = "a"; o["1"] = "b";

Same key: o is {"1": "b"}.

const m = new Map(); m.set(1, "a"); m.set("1", "b");

Two entries: Map keeps the types apart.

Your turn

Key by an object safely.

const byPoint = new ();
byPoint.set(point, value);

The trap

Object.keys returns strings even for numeric keys, so keys.map(k => k + 1) concatenates.

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