isPlainObject

Checks whether a value is a plain object. A plain object is one created with {} or new Object(), where the prototype is exactly Object.prototype.

This helper excludes null, arrays, class instances, and objects with custom prototypes. It never throws and never mutates input.

Signature

function isPlainObject(value: unknown): value is object

Parameters

Name	Data type	Description
value	unknown	The value to check. Must be a non‑null object whose prototype is exactly Object.prototype to return true

Returns

A boolean:

• true: If the value is a non‑null object with Object.prototype as its prototype.
• false: Otherwise.

Examples

isPlainObject({})                     // true
isPlainObject({ a: 1 })               // true
isPlainObject(new Object())           // true

isPlainObject([])                     // false
isPlainObject(null)                   // false
isPlainObject(Object.create(null))    // false
isPlainObject(new Date())             // false
isPlainObject(class X {})             // false
isPlainObject(new (class Y {})())     // false

Notes

• This helper is stricter than isObject. Use isObject if you only need to exclude null and arrays.
• Use normalizeObject if you need to ensure the value becomes an object.
• Use validateObject if you need a Result<T> instead of a boolean.

Next up

isRecord