Check if a value is a plain object

Return true for objects whose prototype is Object.prototype or null.

JavaScript Version 1.0.0 · MIT · .md

function isPlainObject(value) { return value !== null && typeof value === 'object' && [null, Object.prototype].includes(Object.getPrototypeOf(value)); }

Input & expected output

{
  "a": 1
}

true

The edge case

[]

false

Know the limits

• Uses Object.getPrototypeOf instead of the __proto__ accessor, which an own "__proto__" key can shadow.
• JSON cannot create class instances; in code, instances of classes return false.

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.