Check Whether a JavaScript Object Is Empty: Define Which Keys Count

The task

Check an ordinary empty record, then add a hidden property and a symbol. Restrict the helper’s meaning to own properties; it is not a universal emptiness test for Maps, arrays or arbitrary class instances.

Runnable Node 22 example

const assert = require('node:assert/strict');

const record = {};
assert.equal(Object.keys(record).length, 0);
Object.defineProperty(record, 'internal', {value: 7, enumerable: false});
record[Symbol('tag')] = 'memo';
assert.deepEqual(Object.keys(record), []);
assert.equal(Reflect.ownKeys(record).length, 2);
const inherited = Object.create({shared: true});
assert.equal(Object.keys(inherited).length, 0);
assert.equal(Reflect.ownKeys(inherited).length, 0);
console.log(`visible=${Object.keys(record).length}; own=${Reflect.ownKeys(record).length}`);

Expected output and explanation

The visible-key check still reports zero after both additions because neither is an enumerable string key. The all-own-key check reports two. Both observations can be correct under different definitions of empty.

The inherited example has no own keys even though property lookup can find shared. An own-key check answers what belongs directly to that object, not whether lookup can find any value through its prototype. This is why key enumeration should be chosen from the intended contract.

Pitfall to check

Guard against null or undefined before calling an object-enumeration helper. For a Map, size is the relevant entry count; Object.keys(map) would answer a different question. State the supported input shape in a reusable helper.