set

Sets a nested value on an object using a dot-notation path. Non-mutating: returns a new object with only the nodes on the path cloned (structural sharing).

Import

import { set } from "1o1-utils";

import { set } from "1o1-utils/set";

Signature

function set<T extends Record<string, unknown>>({ obj, path, value, objectify }: SetParams<T>): Record<string, unknown>

Parameters

Name	Type	Required	Description
obj	T	Yes	The source object
path	string	Yes	Dot-notation path (e.g. "address.city")
value	unknown	Yes	The value to write at path
objectify	boolean	No	When true, numeric segments create objects with string keys instead of arrays (default false)

Returns

Record<string, unknown> — A new object with value set at path. Input is never mutated.

Examples

set({ obj: { a: { b: 1 } }, path: "a.b", value: 2 });
// => { a: { b: 2 } }

// Numeric segments create arrays by default
set({ obj: {}, path: "items.0.name", value: "x" });
// => { items: [{ name: "x" }] }

// Force plain objects with objectify
set({ obj: {}, path: "items.0.name", value: "x", objectify: true });
// => { items: { "0": { name: "x" } } }

Edge Cases

• Throws if obj is not an object, path is not a string, or path is empty.
• Does not mutate the input — only nodes on the path are cloned; siblings keep their reference.
• Creates missing intermediate containers: arrays when the next segment is numeric (default), objects otherwise. Set objectify: true to always create objects.
• Overwrites intermediate primitives (null, strings, numbers) with fresh objects/arrays.

Also known as

write nested, dot notation, deep set, property path, immutable set, lodash set

Prompt suggestion

I'm using 1o1-utils (npm: https://www.npmjs.com/package/1o1-utils, GitHub: https://github.com/pedrotroccoli/1o1-utils, LLM context: https://pedrotroccoli.github.io/1o1-utils/llms.txt). Show me how to use set to immutably update a deeply nested field in a Redux-style state