added time method call snippet

Author: bahmutov

README.md

@@ -16,6 +16,7 @@ Read [Code Snippets tutorial][1] and
 * [first-paint.js](first-paint.js) - time from page reload to first visible contents.
 * [timing.js](timing.js) - Detailed page timing information, 
 from [addyosmani/timing.js](https://github.com/addyosmani/timing.js).
+* [time-method-call.js](time-method-call.js) - measures single method call time.
 * [local-storage-size.js](local-storage-size.js) - measures size of the strings in the `localStorage`.
 * [expensive-keys.js](expensive-keys.js) - measures how much space individual keys and their values
 take up in a collection of objects, read [Measuring Space Allocation][measure].

time-method-call.js

@@ -0,0 +1,13 @@
+(function profileMethodCall() {
+  var object = primesApp;
+  var methodName = 'findFirstPrimes';
+  var originalMethod = object[methodName];
+  console.assert(typeof originalMethod === 'function', 'cannot find method ' + methodName);
+  object[methodName] = function () {
+    console.time(methodName);
+    originalMethod.call(object);
+    console.timeEnd(methodName);
+    // restore original methodName
+    object[methodName] = originalMethod;
+  };
+}());