RequireAtLeastOne: Make other given keys optional (#142)

sindresorhus · Nov 16, 2020 · 6110607 · 6110607
1 parent 00e04c7
commit 6110607
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Showing 2 changed files with 29 additions and 13 deletions.
diff --git a/source/require-at-least-one.d.ts b/source/require-at-least-one.d.ts
@@ -20,13 +20,14 @@ const responder: RequireAtLeastOne<Responder, 'text' | 'json'> = {
 };
 ```
 */
-export type RequireAtLeastOne<ObjectType, KeysType extends keyof ObjectType = keyof ObjectType> =
-	{
-		// For each Key in KeysType make a mapped type
-		[Key in KeysType]: (
-			// …by picking that Key's type and making it required
-			Required<Pick<ObjectType, Key>>
-		)
-	}[KeysType]
-	// …then, make intersection types by adding the remaining keys to each mapped type.
-	& Except<ObjectType, KeysType>;
+export type RequireAtLeastOne<
+	ObjectType,
+	KeysType extends keyof ObjectType = keyof ObjectType
+> = {
+	// For each `Key` in `KeysType` make a mapped type:
+	[Key in KeysType]-?: Required<Pick<ObjectType, Key>> & // 1. Make `Key`'s type required
+		// 2. Make all other keys in `KeysType` optional
+		Partial<Pick<ObjectType, Exclude<KeysType, Key>>>;
+}[KeysType] &
+	// 3. Add the remaining keys not in `KeysType`
+	Except<ObjectType, KeysType>;
diff --git a/test-d/require-at-least-one.ts b/test-d/require-at-least-one.ts
@@ -11,7 +11,12 @@ type SystemMessages = {
 	optional?: string;
 };
 
-type ValidMessages = RequireAtLeastOne<SystemMessages, 'macos' | 'linux' | 'windows'>;
+type MessageBoard<M> = (messages: M) => string;
+
+type ValidMessages = RequireAtLeastOne<
+	SystemMessages,
+	'macos' | 'linux' | 'windows'
+>;
 const test = (_: ValidMessages): void => {}; // eslint-disable-line @typescript-eslint/no-empty-function
 
 test({macos: 'hey', default: 'hello'});
@@ -22,5 +27,15 @@ expectError(test({}));
 expectError(test({macos: 'hey'}));
 expectError(test({default: 'hello'}));
 
-declare const atLeastOneWithoutKeys: RequireAtLeastOne<{a: number; b: number}>;
-expectAssignable<{a: number; b?: number} | {a?: number; b: number}>(atLeastOneWithoutKeys);
+declare const atLeastOneWithoutKeys: RequireAtLeastOne<{
+	a: number;
+	b: number;
+}>;
+expectAssignable<{a: number; b?: number} | {a?: number; b: number}>(
+	atLeastOneWithoutKeys
+);
+
+expectAssignable<MessageBoard<ValidMessages>>(
+	({macos = '', linux = '🐧', windows = '⊞'}) =>
+		`${linux} + ${windows} = ${macos}`
+);