set

Sets a value in an object at the given path, creating intermediate objects as needed.

Two path forms are supported:

1. String path — dot notation and bracket notation, mixed freely.

   • Dot segments are always string keys: 'layers.1.name' → keys ['layers', '1', 'name'].
   • Bracket segments are always number keys: 'layers[1].name' → keys ['layers', 1, 'name'].
   • String literal paths give full compile-time type inference on the return type.
   • Dynamic (non-literal) strings return T (same object type).

2. Key array (PropertyKey[]) — explicit array of string | number | symbol keys, no parsing performed. Enables symbol-keyed access and precise return-type inference.

Both forms support all objects (plain objects, arrays, class instances). Symbol keys are only reachable via the key-array form.

Intermediate nodes that are absent, null, or not an object are replaced with {}. Any path containing a string segment equal to __proto__, constructor, or prototype is rejected and the original object is returned unchanged (prototype-pollution guard).

Available since v1.9.0

Import

import { set } from '@helpers4/object';
// or, from the all-in-one package (same code, one install):
import { set } from 'helpers4/object';

Signature

set<T extends object, P extends string | readonly PropertyKey[], V extends unknown>(obj: T, path: P, value: V): conditional

Parameters

Parameter	Type	Description
obj	T	The object to mutate
path	P	Dot/bracket-notation string literal or explicit `PropertyKey[]`
value	V	Value to assign at the path

Returns

conditional — The mutated object (same reference, narrowed type)

Examples

Set a nested property (dot notation)

Creates intermediate objects as needed. All segments are string keys — including numeric-looking ones like “1”.

set({}, 'a.b.c', 42)
// => { a: { b: { c: 42 } } }

set({}, 'layers.1.name', 'bg')
// => { layers: { '1': { name: 'bg' } } }   // '1' is a string key

Set via bracket notation

Square-bracket indices become numeric keys. Useful when the path targets an array element.

const obj = { layers: [{}, { name: 'old' }] }
set(obj, 'layers[1].name', 'new')
// => { layers: [{}, { name: 'new' }] }

Set via key array (supports symbols)

Pass an explicit PropertyKey[] to bypass parsing. Supports string, number, and symbol keys.

const id = Symbol('id')
set({}, ['user', id], 'alice')
// => { user: { [id]: 'alice' } }

Source

View source on GitHub