Check if an Object or Array is Empty

easy

By FrontendAtlas Editorial · Updated Jan 30, 2026

Implement isEmpty(obj) that returns true only if the input is an object or array with no own keys/elements, and false otherwise. For non-object/array inputs (like numbers or strings), the function should throw a TypeError. Concepts: objects, arrays, validation.

Arguments

obj: Object | Array — An object or array parsed from JSON.

Returns

boolean —

Returns true if the object/array is empty; otherwise false.

Examples

// Example 1
isEmpty({ x: 5, y: 42 }); // => false

// Example 2
isEmpty({}); // => true

// Example 3
isEmpty([null, false, 0]); // => false

// Example 4
isEmpty([]); // => true

Solution

Overview

Goal: implement isEmpty(obj) so that it returns true only when the input is an array with length 0 or an object whose own enumerable keys list is empty, and throws a TypeError for non-object/array inputs. Key concepts: objects, arrays, validation.

Approach: Handle arrays and objects separately

**Array check:** If Array.isArray(obj) is true, simply return whether obj.length === 0.
**Object check:** If obj is non-null and typeof obj === 'object', get its own enumerable keys with Object.keys(obj) and check if that list is empty.
**Invalid input:** For any other type (number, string, boolean, etc.), throw a TypeError to signal misuse.
**Return result:** Return a boolean indicating emptiness for arrays/objects.

export default function isEmpty(obj) {
  if (Array.isArray(obj)) return obj.length === 0;
  if (obj && typeof obj === 'object') return Object.keys(obj).length === 0;
  throw new TypeError('Expected object or array');
}

export default function isEmpty(obj: Record<string, any> | any[]): boolean {
  if (Array.isArray(obj)) return obj.length === 0;
  if (obj && typeof obj === 'object') return Object.keys(obj).length === 0;
  throw new TypeError('Expected object or array');
}

Notes & Pitfalls

Pitfalls

Checking `Object.keys()` on `null` or `undefined` will throw — always guard with `obj && typeof obj === 'object'`.
Strings also have `.length`, but should not be considered valid inputs here (this implementation throws `TypeError` for them).
Prototype-inherited properties are ignored by `Object.keys()`, which is correct for this task.

Edge cases

`[]` → true (no elements).
`{}` → true (no keys).
`[null, false, 0]` → false (contains items even if falsy).
`Object.create(null)` → true (no enumerable keys).
Non-object/array inputs like `42` or `'hi'` → `TypeError`.

Techniques

Use `Array.isArray()` for accurate array detection.
Prefer `Object.keys()` over `for...in` to ignore prototype properties.

Common mistakes on this challenge

isEmpty should branch arrays, objects, and invalid inputs
This utility needs explicit runtime type handling before checking emptiness.
- Return `obj.length === 0` for arrays.
- For plain objects, use `Object.keys(obj).length === 0`.
- Throw `TypeError` for non-object/non-array inputs.

Resources

Guides

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