Check if an object is an array

Use Array.isArray, which works across realms.

JavaScript Version 1.0.0 · MIT · .md

function isArray(value) { return Array.isArray(value); }

Input & expected output

[]

true

The edge case

{}

false

Know the limits

• Prefer Array.isArray to instanceof Array, which fails for arrays from another frame.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Check whether all values are equal — Compare every item with the first using Object.is.
• Check whether an object is empty — Check for own enumerable string keys on a JSON object.
• Check whether an integer is even — Test parity for safe integers, including zero and negative values.