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- import {Except} from './except';
- import {Simplify} from './simplify';
- /**
- 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](https://github.com/sindresorhus/pageres/blob/4a5d05fca19a5fbd2f53842cbf3eb7b1b63bddd2/source/index.ts#L72), [edit `readonly` objects within tests](https://stackoverflow.com/questions/50703834), [construct a `readonly` object within a function](https://github.com/Microsoft/TypeScript/issues/24509), or to define a single model where the only thing that changes is whether or not some of the keys are mutable.
- @example
- ```
- import {Mutable} 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 mutableFoo: Mutable<Foo> = {a: 1, b: ['2']};
- mutableFoo.a = 3;
- mutableFoo.b[0] = 'new value'; // Will still fail as the value of property "b" is still a readonly type.
- mutableFoo.b = ['something']; // Will work as the "b" property itself is no longer readonly.
- type SomeMutable = Mutable<Foo, 'b' | 'c'>;
- // type SomeMutable = {
- // readonly a: number;
- // b: readonly string[]; // It's now mutable. The type of the property remains unaffected.
- // c: boolean; // It's now mutable.
- // }
- ```
- */
- export type Mutable<BaseType, Keys extends keyof BaseType = keyof BaseType> =
- Simplify<
- // Pick just the keys that are not mutable from the base type.
- Except<BaseType, Keys> &
- // Pick the keys that should be mutable from the base type and make them mutable by removing the `readonly` modifier from the key.
- {-readonly [KeyType in keyof Pick<BaseType, Keys>]: Pick<BaseType, Keys>[KeyType]}
- >;
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