How do you check if an object is empty?

Object.keys(obj).length === 0 is the usual answer, and it is right for plain data objects:

const isEmpty = (obj) => Object.keys(obj).length === 0;

isEmpty({});          // true
isEmpty({ a: 1 });    // false

Why obj === {} never works

Objects compare by reference, so a fresh literal is never equal to anything. JSON.stringify(obj) === "{}" does work but is slow and misleading — it also reports { a: undefined } as empty, because undefined values are dropped during serialisation.

What Object.keys misses

It returns only own, enumerable, string keys. An object can be non-empty in ways it does not see:

Object.keys({ [Symbol("id")]: 1 }).length;                    // 0
Object.keys(Object.defineProperty({}, "a", { value: 1 }));    // [] — non-enumerable

For a stricter check:

const isTrulyEmpty = (obj) => Reflect.ownKeys(obj).length === 0;

Reflect.ownKeys includes symbols and non-enumerable keys.

Guard the input

Object.keys(null) throws, so check the value is an object first:

const isEmptyObject = (v) =>
  v !== null && typeof v === "object" && Object.keys(v).length === 0;

Other types need other checks

arr.length === 0;      // arrays — Object.keys works but is wasteful
map.size === 0;        // Map and Set have .size, not .length or keys
str.trim() === "";     // strings

Object.keys(new Map([["a", 1]])).length is 0, because Map entries are not properties — a subtle bug if a generic "isEmpty" helper is used on one.

For a quick exit on large objects, for (const k in obj) return false stops at the first key instead of building an array, though the difference rarely matters in practice.