41 lines
1.8 KiB
TypeScript
41 lines
1.8 KiB
TypeScript
import type {Except} from './except';
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import type {Simplify} from './simplify';
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/**
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Create a type that strips `readonly` from all or some of an object's keys. Inverse of `Readonly<T>`.
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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 writable.
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@example
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```
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import type {Writable} from 'type-fest';
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type Foo = {
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readonly a: number;
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readonly b: readonly string[]; // To show that only the mutability status of the properties, not their values, are affected.
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readonly c: boolean;
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};
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const writableFoo: Writable<Foo> = {a: 1, b: ['2'], c: true};
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writableFoo.a = 3;
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writableFoo.b[0] = 'new value'; // Will still fail as the value of property "b" is still a readonly type.
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writableFoo.b = ['something']; // Will work as the "b" property itself is no longer readonly.
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type SomeWritable = Writable<Foo, 'b' | 'c'>;
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// type SomeWritable = {
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// readonly a: number;
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// b: readonly string[]; // It's now writable. The type of the property remains unaffected.
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// c: boolean; // It's now writable.
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// }
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```
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@category Object
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*/
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export type Writable<BaseType, Keys extends keyof BaseType = keyof BaseType> =
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Simplify<
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// Pick just the keys that are not writable from the base type.
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Except<BaseType, Keys> &
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// Pick the keys that should be writable from the base type and make them writable by removing the `readonly` modifier from the key.
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{-readonly [KeyType in keyof Pick<BaseType, Keys>]: Pick<BaseType, Keys>[KeyType]}
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>;
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