JavaScript · Language basics

for…in

Iterates enumerable property names, including inherited ones. Use Object.keys for own keys only.

javascriptRunnable example javascript course

Syntax

for (const key in object) { … }

Example

Try it

const scores = { html: 90, css: 85 };
for (const key in scores) console.log(key, scores[key]);

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.