Add 'every' type predicate

readme.md

@@ -234,6 +234,39 @@ if (isSuccess(message)) {
 }
 ```
 
+### `every()
+
+Runtime array type validation. Checks each element of an array.
+
+```ts
+let arr: unknown[] = [1, 2, 3];
+if (every(isNumber)(arr)) {
+  let typeCheck: number[] = arr;
+}
+```
+
+Works with any narrowing validator, including schemas.
+
+```ts
+interface TestInterface {
+  id: number;
+  name: string;
+}
+
+const isTestInterface = schema<TestInterface>({
+  id: isNumber,
+  name: isString
+});
+
+let arr: unknown[] = [{ id: 1, name: 'aaa' }];
+
+if (every(isTestInterface)(arr)) {
+  let typeCheck: TestInterface[] = arr;
+}
+```
+
+```
+
 ## Version
 
 - 1.1.0
@@ -247,3 +280,4 @@ if (isSuccess(message)) {
 - 1.4.0
   - replace ~~`isValidObject()`~~ with `schema()`
   - add `literal()`
+```

src/index.ts

@@ -92,3 +92,12 @@ export function schema<T>(schema: SchemaType<T>): Predicate<T> {
     return false;
   };
 }
+
+export function every<T>(predicate: Predicate<T>): Predicate<T[]> {
+  return function (value: unknown): value is T[] {
+    if (Array.isArray(value)) {
+      return value.every(predicate);
+    }
+    return false;
+  };
+}

test/every.test.ts

@@ -0,0 +1,82 @@
+import { schema, literal, every, isString, isNumber } from '../src/index';
+
+test('fails when array contains elements of an unassignable type', () => {
+  expect(every(isString)([1, 2, 3])).toBe(false);
+  expect(every(isNumber)([1, '2', 3])).toBe(false);
+});
+
+test('passes when array contains correct type', () => {
+  expect(every(isNumber)([1, 2, 3])).toBe(true);
+  expect(every(isString)(['1', '2', '3'])).toBe(true);
+});
+
+test('passes when array is empty', () => {
+  expect(every(isString)([])).toBe(true);
+  expect(every(isNumber)([])).toBe(true);
+});
+
+interface TestInterface {
+  kind: 'test';
+  value: {
+    nestedString: string;
+    nestedNumber: number;
+  };
+}
+
+const isTestInterface = schema<TestInterface>({
+  kind: literal('test'),
+  value: schema<TestInterface['value']>({
+    nestedString: isString,
+    nestedNumber: isNumber
+  })
+});
+
+test('passes when array contains valid objects', () => {
+  expect(
+    every<TestInterface>(isTestInterface)([
+      {
+        kind: 'test',
+        value: {
+          nestedString: 'string',
+          nestedNumber: 1
+        }
+      }
+    ])
+  ).toBe(true);
+});
+
+test('fails when array contains invalid objects', () => {
+  expect(
+    every<TestInterface>(isTestInterface)([
+      {
+        kind: 'test',
+        value: {
+          nested_string: 'string'
+        }
+      }
+    ])
+  ).toBe(false);
+});
+
+every<string>(isString);
+
+let arr: unknown[] = [1, 2, 3];
+if (every(isNumber)(arr)) {
+  let typeCheck: number[] = arr;
+}
+
+interface TestInterfaceT {
+  id: number;
+  name: string;
+}
+
+const isTestInterfaceT = schema<TestInterfaceT>({
+  id: isNumber,
+  name: isString
+});
+
+let arr2: unknown[] = [{ id: 1, name: 'aaa' }];
+
+if (every(isTestInterfaceT)(arr2)) {
+  let typeCheck: TestInterfaceT[] = arr2;
+}