isClassInstance

Checks whether a value is a constructed object rather than a plain object literal, an array, or a primitive. Use it when behavior depends on a value carrying a prototype, such as deciding whether to rebuild methods after parsing, choosing between structural and instance-aware comparison, or refusing to merge configuration into something that is not a plain record.

The check is prototype-based, not user-defined-class-based, so built-in types count as instances. Date, Map, Set, URL, RegExp, and Luxon's DateTime all return true alongside your own classes.

The function is a type guard for object, which narrows away null, arrays, and primitives in the true branch.

Importing

import { isClassInstance } from '@almighty-shogun/utils';

Usage

import { isClassInstance } from '@almighty-shogun/utils';

class Point {
    constructor(public x = 0, public y = 0) {}
}

isClassInstance(new Point());   // true
isClassInstance(new Date());    // true
isClassInstance({ x: 0 });      // false
isClassInstance([1, 2]);        // false
isClassInstance(null);          // false
isClassInstance('text');        // false

Edge cases

An object created with no prototype has no constructor, so it is reported as an instance:

import { isClassInstance } from '@almighty-shogun/utils';

isClassInstance(Object.create(null));

// true

That suits callers who use the result to mean "not a plain record", which is how deserialize uses it. Add an explicit Object.getPrototypeOf(value) !== null check when a null-prototype object should be treated as plain.

Parameters

value: unknown
Value to test.

Returns

true when the value is an object built from a constructor other than Object.

Uses

• hasValue

Type signature

declare function isClassInstance(value: unknown): value is object;