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JavaScript Tutorial

Variables to closures, promises, the DOM and OOP — a complete JS reference.

Object.keys()

Returns an array of an object's own enumerable property names, in the same order Object.entries() and for...in would visit them.

const user = { name: 'Ada', age: 30 };
Object.keys(user); // ['name', 'age']
Object.keys(user).length; // 2 — common way to count properties
  • Only own properties — inherited/prototype properties are excluded
  • Pairs naturally with .map()/.forEach() to iterate an object's keys
  • Object.values() and Object.entries() are the companion methods for values and [key,value] pairs