Add assertion utilities

assets/js/utils/__tests__/assert.spec.ts

@@ -0,0 +1,35 @@
+import { assertNotNull, assertNotUndefined, assertType } from '../assert';
+
+describe('Assertion utilities', () => {
+  describe('assertNotNull', () => {
+    it('should return non-null values', () => {
+      expect(assertNotNull(1)).toEqual(1);
+      expect(assertNotNull('anything')).toEqual('anything');
+    });
+
+    it('should throw when passed a null value', () => {
+      expect(() => assertNotNull(null)).toThrow('Expected non-null value');
+    });
+  });
+
+  describe('assertNotUndefined', () => {
+    it('should return non-undefined values', () => {
+      expect(assertNotUndefined(1)).toEqual(1);
+      expect(assertNotUndefined('anything')).toEqual('anything');
+    });
+
+    it('should throw when passed an undefined value', () => {
+      expect(() => assertNotUndefined(undefined)).toThrow('Expected non-undefined value');
+    });
+  });
+
+  describe('assertType', () => {
+    it('should return values of the generic type', () => {
+      expect(assertType({}, Object)).toEqual({});
+    });
+
+    it('should throw when passed a value of the wrong type', () => {
+      expect(() => assertType('anything', Number)).toThrow('Expected value of type');
+    });
+  });
+});

assets/js/utils/assert.ts

@@ -0,0 +1,28 @@
+export function assertNotNull<T>(value: T | null): T {
+  if (value === null) {
+    throw new Error('Expected non-null value');
+  }
+
+  return value;
+}
+
+export function assertNotUndefined<T>(value: T | undefined): T {
+  // eslint-disable-next-line no-undefined
+  if (value === undefined) {
+    throw new Error('Expected non-undefined value');
+  }
+
+  return value;
+}
+
+/* eslint-disable @typescript-eslint/no-explicit-any */
+type Constructor<T> = { new (...args: any[]): T };
+
+export function assertType<T>(value: any, c: Constructor<T>): T {
+  if (value instanceof c) {
+    return value;
+  }
+
+  throw new Error('Expected value of type');
+}
+/* eslint-enable @typescript-eslint/no-explicit-any */