Function setIn

Immutably sets a value at a nested path, returning a new root object.

Supports plain objects, arrays (including negative indices), and Maps.
Clones only the containers on the updated path (structural sharing).
Unaffected sibling branches retain their original references.
Missing intermediate containers are auto-created as {} or [] depending on whether the next key is numeric.
Every position in the path tuple is autocompleted and type-checked by the language server for known types.
Paths up to depth 6 have fully inferred return types. Deeper paths compile without error but return unknown.

Note: For dynamic paths or paths that create fields not present in the original type, the return type falls back to unknown. Use type assertions when needed.

Example: Basic nested update

const data = { user: { profile: { name: 'Alice' } } };
const updated = setIn(data, ['user', 'profile', 'name'], 'Bob');
// { user: { profile: { name: 'Bob' } } }
// Original data.user.profile.name is still 'Alice'

Example: Updating array elements

const data = { items: [{ id: 1 }, { id: 2 }] };
const updated = setIn(data, ['items', 1, 'id'], 99);
// { items: [{ id: 1 }, { id: 99 }] }

Example: Negative array index (Python-style)

const data = { tags: ['a', 'b', 'c'] };
const updated = setIn(data, ['tags', -1], 'z');
// { tags: ['a', 'b', 'z'] }

Example: Creating missing intermediate paths

const data = {};
const updated = setIn(data, ['user', 'profile', 'name'], 'Alice');
// { user: { profile: { name: 'Alice' } } }

Example: Creating arrays when path contains numeric keys

const data = {};
const updated = setIn(data, ['items', 0, 'value'], 'first');
// { items: [{ value: 'first' }] }

Example: With a Map

const map = new Map([['user', { score: 100 }]]);
const updated = setIn(map, ['user', 'score'], 200);
// Map has {user: { score: 200 }}; original map unchanged

Example: Deeply nested arrays

const data = { matrix: [[1, 2], [3, 4]] };
const updated = setIn(data, ['matrix', 1, 0], 99);
// { matrix: [[1, 2], [99, 4]] }

Template: T

The root object type.

Template: V

The type of the value to set.

Param: object

The root value to update immutably.

Param: path

Tuple of string keys or numeric indices describing the path.

Param: value

The value to set at the given path.

Returns

A new root object with the value set at the specified path. Original object is unchanged.

setIn<T, V>(object: T, path: [], value: V): V
Type Parameters
- T
- V
Parameters
- object: T
- path: []
- value: V
Returns V
- Defined in core/set-in.ts:77
setIn<T, K0 extends string | number, V extends unknown>(
    object: T,
    path: [K0],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0]
- value: V
Returns T
- Defined in core/set-in.ts:79
setIn<
    T,
    K0 extends string | number,
    K1 extends string | number,
    V extends unknown,
>(
    object: T,
    path: [K0, K1],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- K1 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0, K1]
- value: V
Returns T
- Defined in core/set-in.ts:85
setIn<
    T,
    K0 extends string | number,
    K1 extends string | number,
    K2 extends string | number,
    V extends unknown,
>(
    object: T,
    path: [K0, K1, K2],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- K1 extends string | number
- K2 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0, K1, K2]
- value: V
Returns T
- Defined in core/set-in.ts:92
setIn<
    T,
    K0 extends string | number,
    K1 extends string | number,
    K2 extends string | number,
    K3 extends string | number,
    V extends unknown,
>(
    object: T,
    path: [K0, K1, K2, K3],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- K1 extends string | number
- K2 extends string | number
- K3 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0, K1, K2, K3]
- value: V
Returns T
- Defined in core/set-in.ts:100
setIn<
    T,
    K0 extends string | number,
    K1 extends string | number,
    K2 extends string | number,
    K3 extends string | number,
    K4 extends string | number,
    V extends unknown,
>(
    object: T,
    path: [K0, K1, K2, K3, K4],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- K1 extends string | number
- K2 extends string | number
- K3 extends string | number
- K4 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0, K1, K2, K3, K4]
- value: V
Returns T
- Defined in core/set-in.ts:109
setIn<
    T,
    K0 extends string | number,
    K1 extends string | number,
    K2 extends string | number,
    K3 extends string | number,
    K4 extends string | number,
    K5 extends string | number,
    V extends unknown,
>(
    object: T,
    path: [K0, K1, K2, K3, K4, K5],
    value: V,
): T
Type Parameters
- T
- K0 extends string | number
- K1 extends string | number
- K2 extends string | number
- K3 extends string | number
- K4 extends string | number
- K5 extends string | number
- V extends unknown
Parameters
- object: T
- path: [K0, K1, K2, K3, K4, K5]
- value: V
Returns T
- Defined in core/set-in.ts:119
setIn<T, V>(object: T, path: readonly (string | number)[], value: V): unknown
Type Parameters
- T
- V
Parameters
- object: T
- path: readonly (string | number)[]
- value: V
Returns unknown
- Defined in core/set-in.ts:130
setIn(
    object: unknown,
    path: [
        string
        | number,
        string | number,
        string | number,
        string | number,
        string | number,
        string | number,
        string | number,
        ...(string | number)[],
    ],
    value: unknown,
): unknown
Parameters
- object: unknown
- path: [
      string
      | number,
      string | number,
      string | number,
      string | number,
      string | number,
      string | number,
      string | number,
      ...(string | number)[],
  ]
- value: unknown
Returns unknown
- Defined in core/set-in.ts:132

Function setIn

Example: Basic nested update

Example: Updating array elements

Example: Negative array index (Python-style)

Example: Creating missing intermediate paths

Example: Creating arrays when path contains numeric keys

Example: With a Map

Example: Deeply nested arrays

Template: T

Template: V

Param: object

Param: path

Param: value

Returns

Type Parameters

Parameters

Returns V

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns T

Type Parameters

Parameters

Returns unknown

Parameters

Returns unknown

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