feat(js-core): add isPromiseLike()

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

@@ -7,6 +7,7 @@ import {
   elapsedToString,
   isDefined,
   isEqualAtDepth,
+  isPromiseLike,
   isSetEqual,
   isSuperset,
   mapAsKeys,
@@ -70,6 +71,10 @@ describe('js-core', () => {
     expect(isEqualAtDepth).toBeDefined();
   });
 
+  it('has isPromiseLike', () => {
+    expect(isPromiseLike).toBeDefined();
+  });
+
   it('has isSetEqual', () => {
     expect(isSetEqual).toBeDefined();
   });

projects/js-core/src/lib/is-defined.spec.ts

@@ -1,12 +1,11 @@
 import { isDefined } from './is-defined';
 
 describe('isDefined()', () => {
-  it('works', () => {
-    // tslint:disable-next-line:only-arrow-functions
-    const args = (function (..._: any[]): IArguments {
-      return arguments;
-    })([1, 2, 3]);
+  function getArguments(): IArguments {
+    return arguments;
+  }
 
+  it('works', () => {
     // falsey values
     expect(isDefined(undefined)).toBe(false);
     expect(isDefined(null)).toBe(true);
@@ -16,7 +15,7 @@ describe('isDefined()', () => {
     expect(isDefined('')).toBe(true);
 
     // all the other things
-    expect(isDefined(args)).toBe(true);
+    expect(isDefined(getArguments())).toBe(true);
     expect(isDefined([1, 2, 3])).toBe(true);
     expect(isDefined(true)).toBe(true);
     expect(isDefined(new Date())).toBe(true);

projects/js-core/src/lib/is-promise-like.spec.ts

@@ -0,0 +1,33 @@
+import { isPromiseLike } from './is-promise-like';
+
+describe('isPromiseLike()', () => {
+  function getArguments(): IArguments {
+    return arguments;
+  }
+
+  it('works', () => {
+    expect(isPromiseLike(Promise.resolve('hi'))).toBe(true);
+    expect(isPromiseLike(Promise.reject('bye'))).toBe(true);
+
+    // falsey values
+    expect(isPromiseLike(undefined)).toBe(false);
+    expect(isPromiseLike(null)).toBe(false);
+    expect(isPromiseLike(false)).toBe(false);
+    expect(isPromiseLike(0)).toBe(false);
+    expect(isPromiseLike(NaN)).toBe(false);
+    expect(isPromiseLike('')).toBe(false);
+
+    // all the other things
+    expect(isPromiseLike(getArguments())).toBe(false);
+    expect(isPromiseLike([1, 2, 3])).toBe(false);
+    expect(isPromiseLike(true)).toBe(false);
+    expect(isPromiseLike(new Date())).toBe(false);
+    expect(isPromiseLike(new Error())).toBe(false);
+    expect(isPromiseLike(Array.prototype.slice)).toBe(false);
+    expect(isPromiseLike({ a: 1 })).toBe(false);
+    expect(isPromiseLike(1)).toBe(false);
+    expect(isPromiseLike(/x/)).toBe(false);
+    expect(isPromiseLike('a')).toBe(false);
+    expect(isPromiseLike(Symbol('a'))).toBe(false);
+  });
+});

projects/js-core/src/lib/is-promise-like.ts

@@ -0,0 +1,13 @@
+/**
+ * Checks if `value` has a `then()` function, indicating that it is probably promise-like.
+ *
+ * ```ts
+ * isPromiseLike(Promise.resolve('hi')); // true
+ * isPromiseLike(Promise.reject('bye')); // true
+ * isPromiseLike({}); // false
+ * isPromiseLike(null); // false
+ * ```
+ */
+export function isPromiseLike(value: any): value is PromiseLike<unknown> {
+  return typeof value?.then === 'function';
+}

projects/js-core/src/public-api.ts

@@ -8,6 +8,7 @@ export * from './lib/sets';
 export * from './lib/time';
 export { assert } from './lib/assert';
 export { isDefined } from './lib/is-defined';
+export { isPromiseLike } from './lib/is-promise-like';
 export { MigrationManager } from './lib/migration-manager';
 export { Persistence } from './lib/persistence';
 export { roundToMultipleOf } from './lib/round-to-multiple-of';