feat(js-core): add isFalsy()

projects/integration/src/app/api-tests/js-core.spec.ts

@@ -9,6 +9,7 @@ import {
   elapsedToString,
   isDefined,
   isEqualAtDepth,
+  isFalsy,
   isPromiseLike,
   isSetEqual,
   isSuperset,
@@ -80,6 +81,10 @@ describe('js-core', () => {
       expect(isEqualAtDepth).toBeDefined();
     });
 
+    it('has isFalsy', () => {
+      expect(isFalsy).toBeDefined();
+    });
+
     it('has isPromiseLike', () => {
       expect(isPromiseLike).toBeDefined();
     });

projects/js-core/src/lib/predicates/index.ts

@@ -1,3 +1,4 @@
 export { isDefined } from './is-defined';
 export { isEqualAtDepth } from './is-equal-at-depth';
+export { isFalsy } from './is-falsy';
 export { isPromiseLike } from './is-promise-like';

projects/js-core/src/lib/predicates/is-falsy.spec.ts

@@ -0,0 +1,30 @@
+import { isFalsy } from './is-falsy';
+
+describe('isFalsy', () => {
+  it('returns `true` for falsy values', () => {
+    expect(isFalsy(false)).toBe(true);
+    expect(isFalsy(0)).toBe(true);
+    expect(isFalsy(-0)).toBe(true);
+    // uncomment when targeting ES2020
+    // expect(isFalsy(0n)).toBe(true);
+    expect(isFalsy('')).toBe(true);
+    expect(isFalsy(null)).toBe(true);
+    expect(isFalsy(undefined)).toBe(true);
+    expect(isFalsy(NaN)).toBe(true);
+  });
+
+  // tslint:disable-next-line:only-arrow-functions
+  it('returns `false` for truthy values', function (): void {
+    expect(isFalsy(arguments)).toBe(false);
+    expect(isFalsy([1, 2, 3])).toBe(false);
+    expect(isFalsy(true)).toBe(false);
+    expect(isFalsy(new Date())).toBe(false);
+    expect(isFalsy(new Error())).toBe(false);
+    expect(isFalsy(Array.prototype.slice)).toBe(false);
+    expect(isFalsy({ a: 1 })).toBe(false);
+    expect(isFalsy(1)).toBe(false);
+    expect(isFalsy(/x/)).toBe(false);
+    expect(isFalsy('a')).toBe(false);
+    expect(isFalsy(Symbol('a'))).toBe(false);
+  });
+});

projects/js-core/src/lib/predicates/is-falsy.ts

@@ -0,0 +1,6 @@
+/**
+ * Checks if `value` is [falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy).
+ */
+export function isFalsy(value: any): boolean {
+  return !value;
+}