feat: add maybeOptionsOrCallback util method (#315)

Author: JustinBeckwith

core/common/src/util.ts

@@ -740,6 +740,20 @@ export class Util {
 
     return hyphenatedPackageName + '/' + packageJson.version;
   }
+
+  /**
+   * Given two parameters, figure out if this is either:
+   *  - Just a callback function
+   *  - An options object, and then a callback function
+   * @param optionsOrCallback An options object or callback.
+   * @param cb A potentially undefined callback.
+   */
+  maybeOptionsOrCallback<T = {}, C = (err?: Error) => void>(
+      optionsOrCallback?: T|C, cb?: C): [T, C] {
+    return typeof optionsOrCallback === 'function' ?
+        [{} as T, optionsOrCallback as C] :
+        [optionsOrCallback as T, cb as C];
+  }
 }
 
 const util = new Util();

core/common/test/service.ts

@@ -20,7 +20,7 @@ import * as proxyquire from 'proxyquire';
 import {Request, RequestResponse} from 'request';
 
 import {Interceptor} from '../src';
-import {Service, ServiceConfig, ServiceOptions} from '../src/service';
+import {ServiceConfig, ServiceOptions} from '../src/service';
 import {BodyResponseCallback, DecorateRequestOptions, MakeAuthenticatedRequest, MakeAuthenticatedRequestFactoryConfig, util, Util} from '../src/util';
 
 proxyquire.noPreserveCache();

core/common/test/util.ts

@@ -54,7 +54,7 @@ function fakeRequest() {
   return (requestOverride || request).apply(null, arguments);
 }
 
-fakeRequest.defaults = (defaultConfiguration: {}) => {
+fakeRequest.defaults = () => {
   // Ignore the default values, so we don't have to test for them in every API
   // call.
   return fakeRequest;
@@ -1505,4 +1505,22 @@ describe('common/util', () => {
       assert.strictEqual(userAgent, 'gcloud-node-storage/0.1.0');
     });
   });
+
+  describe('maybeOptionsOrCallback', () => {
+    it('should allow passing just a callback', () => {
+      const optionsOrCallback = () => {};
+      const [opts, cb] = util.maybeOptionsOrCallback(optionsOrCallback);
+      assert.strictEqual(optionsOrCallback, cb);
+      assert.deepStrictEqual(opts, {});
+    });
+
+    it('should allow passing both opts and callback', () => {
+      const optionsOrCallback = {};
+      const callback = () => {};
+      const [opts, cb] =
+          util.maybeOptionsOrCallback(optionsOrCallback, callback);
+      assert.strictEqual(opts, optionsOrCallback);
+      assert.strictEqual(cb, callback);
+    });
+  });
 });