throttle should check for valid args (#113)

js/utils/throttle.js

@@ -6,6 +6,12 @@
  * @param  {function} func        function to invoke
  */
 function throttle(throttleTime, func) {
+    if (typeof throttleTime !== 'number' || throttleTime <= 0) {
+        throw Error('throttle: invalid throttleTime arg, must be a number: ' + throttleTime);
+    }
+    if (typeof func !== 'function') {
+        throw Error('throttle: invalid func arg, must be a function: ' + func);
+    }
     let timer, lastInvoke = 0;
     return function() {
         let args = arguments;

tests/utils/throttle.test.js

@@ -55,6 +55,35 @@ describe('throttle tests', function() {
         expect(callback.mock.calls.length).toBe(2);
     });
 
+    describe('expect to throw exception', function() {
+        it('when calling throttle with time equal to zero', function(done) {
+            try {
+                throttle(0, function() {});
+            } catch(error) {
+                expect(error.message).toBeDefined();
+                done();
+            }
+        });
+
+        it('when calling throttle with time less than zero', function(done) {
+            try {
+                throttle(-1, function() {});
+            } catch(error) {
+                expect(error.message).toBeDefined();
+                done();
+            }
+        });
+
+        it('when calling throttle without a function callback', function(done) {
+            try {
+                throttle(1, 'not a func');
+            } catch(error) {
+                expect(error.message).toBeDefined();
+                done();
+            }
+        });
+    });
+
     afterEach(function() {
         // restore orig
         Date.now = origNow;