Add OverrideProperties type (#597)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -72,6 +72,7 @@ export type {StringKeyOf} from './source/string-key-of';
 export type {Exact} from './source/exact';
 export type {ReadonlyTuple} from './source/readonly-tuple';
 export type {OptionalKeysOf} from './source/optional-keys-of';
+export type {OverrideProperties} from './source/override-properties';
 export type {HasOptionalKeys} from './source/has-optional-keys';
 export type {RequiredKeysOf} from './source/required-keys-of';
 export type {HasRequiredKeys} from './source/has-required-keys';

readme.md

@@ -135,6 +135,7 @@ Click the type names for complete docs.
 - [`Merge`](source/merge.d.ts) - Merge two types into a new type. Keys of the second type overrides keys of the first type.
 - [`MergeDeep`](source/merge-deep.d.ts) - Merge two objects or two arrays/tuples recursively into a new type.
 - [`MergeExclusive`](source/merge-exclusive.d.ts) - Create a type that has mutually exclusive keys.
+- [`OverrideProperties`](source/override-properties.d.ts) - Override only existing properties of the given type. Similar to `Merge`, but enforces that the original type has the properties you want to override.
 - [`RequireAtLeastOne`](source/require-at-least-one.d.ts) - Create a type that requires at least one of the given keys.
 - [`RequireExactlyOne`](source/require-exactly-one.d.ts) - Create a type that requires exactly a single key of the given keys and disallows more.
 - [`RequireAllOrNone`](source/require-all-or-none.d.ts) - Create a type that requires all of the given keys or none of the given keys.

source/override-properties.d.ts

@@ -0,0 +1,26 @@
+import type {Merge} from './merge';
+
+/**
+Override existing properties of the given type. Similar to `Merge`, but enforces that the original type has the properties you want to override.
+
+This is useful when you want to override existing properties with a different type and make sure that these properties really exist in the original.
+
+@example
+```
+type Foo = {
+	a: string
+	b: string
+}
+type Bar = OverrideProperties<Foo, {b: number}>
+//=> {a: string, b: number}
+
+type Baz = OverrideProperties<Foo, {c: number}>
+// error TS2559: Type '{c: number}' has no properties in common with type 'Partial{a: unknown; b: unknown}>'.
+```
+
+@category Object
+*/
+export type OverrideProperties<
+	TOriginal,
+	TOverride extends Partial<{[key in keyof TOriginal]: unknown}>,
+> = Merge<TOriginal, TOverride>;

test-d/override-properties.ts

@@ -0,0 +1,14 @@
+import {expectError, expectType} from 'tsd';
+import type {OverrideProperties} from '../source/override-properties';
+
+type Foo = {
+	a: number;
+	b: string;
+};
+
+const fixture: OverrideProperties<Foo, {b: number}> = {a: 1, b: 2};
+expectType<{a: number; b: number}>(fixture);
+
+expectError(() => {
+    type Bar = OverrideProperties<Foo, {c: number}>;
+});