Narrow the searched element type in setHas and arrayIncludes (#41)

sindresorhus · Mar 16, 2022 · 04f2818 · 04f2818
1 parent 18b77d6
commit 04f2818
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Showing 4 changed files with 20 additions and 4 deletions.
diff --git a/source/array-includes.ts b/source/array-includes.ts
@@ -18,9 +18,9 @@ if (arrayIncludes(values, valueToCheck)) {
 @category Improved builtin
 @category Type guard
 */
-export function arrayIncludes<Type>(
+export function arrayIncludes<Type extends SuperType, SuperType = unknown>(
 	array: Type[] | readonly Type[],
-	item: unknown,
+	item: SuperType,
 	fromIndex?: number,
 ): item is Type {
 	return array.includes(item as Type, fromIndex);

diff --git a/source/set-has.ts b/source/set-has.ts
@@ -19,9 +19,9 @@ if (setHas(valueSet, valueToCheck)) {
 @category Improved builtin
 @category Type guard
 */
-export function setHas<Type>(
+export function setHas<Type extends SuperType, SuperType = unknown>(
 	set: ReadonlySet<Type>,
-	item: unknown,
+	item: SuperType,
 ): item is Type {
 	return set.has(item as Type);
 }
diff --git a/test/array-includes.ts b/test/array-includes.ts
@@ -1,14 +1,22 @@
 import test from 'ava';
+import {expectTypeOf} from 'expect-type';
 import {arrayIncludes} from '../source/index.js';
 
 test('arrayIncludes()', t => {
 	const values = ['a', 'b', 'c'] as const;
 	const validValue: unknown = 'a';
 	const invalidValue: unknown = 'd';
+	const invalidTypedValue = 1;
 	let testValueType: typeof values[number];
 
+	expectTypeOf(values).items.toMatchTypeOf<typeof validValue>();
+	expectTypeOf(values).items.toMatchTypeOf<typeof invalidValue>();
+	expectTypeOf(values).items.not.toMatchTypeOf<typeof invalidTypedValue>();
+
 	t.true(arrayIncludes(values, validValue));
 	t.false(arrayIncludes(values, invalidValue));
+	// @ts-expect-error
+	t.false(arrayIncludes(values, invalidTypedValue));
 
 	if (arrayIncludes(values, validValue)) {
 		// @ts-expect-error

diff --git a/test/set-has.ts b/test/set-has.ts
@@ -1,15 +1,23 @@
 import test from 'ava';
+import {expectTypeOf} from 'expect-type';
 import {setHas} from '../source/index.js';
 
 test('setHas()', t => {
 	const values = ['a', 'b', 'c'] as const;
 	const valueSet = new Set(values);
 	const validValue: unknown = 'a';
 	const invalidValue: unknown = 'd';
+	const invalidTypedValue = 1;
 	let testValueType: typeof values[number];
 
+	expectTypeOf(values).items.toMatchTypeOf<typeof validValue>();
+	expectTypeOf(values).items.toMatchTypeOf<typeof invalidValue>();
+	expectTypeOf(values).items.not.toMatchTypeOf<typeof invalidTypedValue>();
+
 	t.true(setHas(valueSet, validValue));
 	t.false(setHas(valueSet, invalidValue));
+	// @ts-expect-error
+	t.false(setHas(valueSet, invalidTypedValue));
 
 	// eslint-disable-next-line unicorn/prefer-ternary
 	if (setHas(valueSet, validValue)) {