Add isPromise(). Closes #346

API.md

@@ -393,3 +393,11 @@ await Hoek.wait(2000); // waits for 2 seconds
 
 #### block()
 A no-op Promise. Does nothing.
+
+
+#### isPromise(promise)
+
+Determines if an item is a promise where:
+- `promise` - the item being tested.
+
+Returns `true` is the item is a promise, otherwise `false`.

lib/index.d.ts

@@ -445,6 +445,16 @@ export function wait(timeout?: number): Promise<void>;
 export function block(): Promise<void>;
 
 
+/**
+ * Determines if an object is a promise.
+ * 
+ * @param promise - the object tested.
+ * 
+ * @returns true if the object is a promise, otherwise false.
+ */
+export function isPromise(promise: any): boolean;
+
+
 export namespace ts {
 
     /**

lib/index.js

@@ -19,6 +19,7 @@ module.exports = {
     flatten: require('./flatten'),
     ignore: require('./ignore'),
     intersect: require('./intersect'),
+    isPromise: require('./isPromise'),
     merge: require('./merge'),
     once: require('./once'),
     reach: require('./reach'),

lib/isPromise.js

@@ -0,0 +1,9 @@
+'use strict';
+
+const internals = {};
+
+
+module.exports = function (promise) {
+
+    return !!promise && typeof promise.then === 'function';
+};

test/index.js

@@ -2767,3 +2767,32 @@ describe('stringify()', () => {
         expect(Hoek.stringify(obj)).to.contain('Cannot display object');
     });
 });
+
+describe('isPromise()', () => {
+
+    it('determines if an object is a promise', async () => {
+
+        expect(Hoek.isPromise({})).to.be.false();
+        expect(Hoek.isPromise(null)).to.be.false();
+        expect(Hoek.isPromise(false)).to.be.false();
+        expect(Hoek.isPromise(0)).to.be.false();
+        expect(Hoek.isPromise('')).to.be.false();
+        expect(Hoek.isPromise({ then: 1 })).to.be.false();
+        expect(Hoek.isPromise([])).to.be.false();
+
+        const items = [
+            Promise.resolve(),
+            Promise.reject()
+        ];
+
+        expect(Hoek.isPromise(items[0])).to.be.true();
+        expect(Hoek.isPromise(items[1])).to.be.true();
+        expect(Hoek.isPromise(new Promise(Hoek.ignore))).to.be.true();
+        expect(Hoek.isPromise({ then: Hoek.ignore })).to.be.true();
+
+        try {
+            await Promise.all(items);
+        }
+        catch (err) { }
+    });
+});

test/index.ts

@@ -322,6 +322,18 @@ expect.error(Hoek.block(123));
 // $lab:types:on$
 
 
+// isPromise()
+
+Hoek.isPromise(1);
+Hoek.isPromise({});
+Hoek.isPromise(null);
+
+expect.type<boolean>(Hoek.isPromise(1));
+
+expect.error(Hoek.isPromise());
+expect.error(Hoek.isPromise(1, 2));
+
+
 // ts
 
 interface X { a: number; };