Type Alias Writable<BaseType, Keys>

Writable: Simplify<
    Except<BaseType, Keys> & {
        -readonly [KeyType in keyof Pick<BaseType, Keys>]: Pick<BaseType, Keys>[KeyType]
    },
>

Create a type that strips readonly from all or some of an object's keys. Inverse of Readonly<T>.

This can be used to store and mutate options within a class, edit readonly objects within tests, construct a readonly object within a function, or to define a single model where the only thing that changes is whether or not some of the keys are writable.

Type Parameters

Example

import type {Writable} from 'type-fest';

type Foo = {
	readonly a: number;
	readonly b: readonly string[]; // To show that only the mutability status of the properties, not their values, are affected.
	readonly c: boolean;
};

const writableFoo: Writable<Foo> = {a: 1, b: ['2'], c: true};
writableFoo.a = 3;
writableFoo.b[0] = 'new value'; // Will still fail as the value of property "b" is still a readonly type.
writableFoo.b = ['something']; // Will work as the "b" property itself is no longer readonly.

type SomeWritable = Writable<Foo, 'b' | 'c'>;
// type SomeWritable = {
// 	readonly a: number;
// 	b: readonly string[]; // It's now writable. The type of the property remains unaffected.
// 	c: boolean; // It's now writable.
// }

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