feat: add type guard isTruthy

Author: spawnia

src/typeGuards.test.ts

@@ -5,12 +5,19 @@ import {
   isNonEmptyString,
   isNotNullish,
   isString,
+  isTruthy,
 } from './typeGuards';
 
 describe('typeGuards', () => {
-  describe('isString', () => {
-    assertTrue(isString, ['foo', '1', 'true', '']);
-    assertFalse(isString, [/foo/, 1, true, null, undefined]);
+  describe('isArrayOfStrings', () => {
+    expect(isArrayOfStrings(['foo', 'bar'])).toBe(true);
+    expect(isArrayOfStrings([])).toBe(true);
+    assertFalse(isArrayOfStrings, [null, undefined, ['', null]]);
+  });
+
+  describe('isEmptyObject', () => {
+    assertTrue(isEmptyObject, [{}]);
+    assertFalse(isEmptyObject, [{ foo: 'bar' }, [], null, undefined, '']);
   });
 
   describe('isNonEmptyString', () => {
@@ -23,14 +30,13 @@ describe('typeGuards', () => {
     assertFalse(isNotNullish, [null, undefined]);
   });
 
-  describe('isArrayOfStrings', () => {
-    expect(isArrayOfStrings(['foo', 'bar'])).toBe(true);
-    expect(isArrayOfStrings([])).toBe(true);
-    assertFalse(isArrayOfStrings, [null, undefined, ['', null]]);
+  describe('isString', () => {
+    assertTrue(isString, ['foo', '1', 'true', '']);
+    assertFalse(isString, [/foo/, 1, true, null, undefined]);
   });
 
-  describe('emptyObject', () => {
-    assertTrue(isEmptyObject, [{}]);
-    assertFalse(isEmptyObject, [{ foo: 'bar' }, [], null, undefined, '']);
+  describe('isTruthy', () => {
+    assertTrue(isTruthy, [true, 1, -1, ' ', '0', 'false', [], {}]);
+    assertFalse(isTruthy, [null, undefined, false, 0, -0, '', document.all]);
   });
 });

src/typeGuards.ts

@@ -1,5 +1,14 @@
-export function isString(value: unknown): value is string {
-  return typeof value === 'string';
+export function isArrayOfStrings(value: unknown): value is Array<string> {
+  return value instanceof Array && value.every(isString);
+}
+
+export function isEmptyObject(value: unknown): value is Record<string, never> {
+  return Boolean(
+    value &&
+      typeof value === 'object' &&
+      !(value instanceof Array) &&
+      Object.keys(value).length === 0,
+  );
 }
 
 export function isNonEmptyString(value: unknown): value is Exclude<string, ''> {
@@ -10,15 +19,16 @@ export function isNotNullish<T>(value: T): value is NonNullable<T> {
   return value != null;
 }
 
-export function isArrayOfStrings(value: unknown): value is Array<string> {
-  return value instanceof Array && value.every(isString);
+export function isString(value: unknown): value is string {
+  return typeof value === 'string';
 }
 
-export function isEmptyObject(value: unknown): value is Record<string, never> {
-  return Boolean(
-    value &&
-      typeof value === 'object' &&
-      !(value instanceof Array) &&
-      Object.keys(value).length === 0,
-  );
+/** https://developer.mozilla.org/en-US/docs/Glossary/Falsy */
+export function isTruthy<T>(
+  value: T,
+): value is Exclude<
+  T,
+  null | undefined | false | 0 | 0n | '' | typeof document.all
+> {
+  return Boolean(value);
 }