137:T607,JavaScript execution speed 287 We define three stopwatches: for the window.onload event and for each mouse listener process. We assign meaningful names to the stopwatches, as these will be used by the report that we generate. Let’s load the modified application, then, and give it a quick spin. When we mouse over the mousemat as before, our profiler is busy collecting data, which we can examine at any point by clicking the profile link in the top left. Figure 8.2 shows the application in the browser after a few hundred mouse moves, with the profiler report showing. On both Firefox and Internet Explorer browsers we can see that in this case, the write status method takes less than one quarter the time of the draw thumbnail method. Note that the window.onload event appears to have executed in 0 ms, owing to the limited granularity of the JavaScript Date object. With this profiling system, we’re working entirely within the JavaScript interpreter, with all of the limitations that apply there. Mozilla browsers can take advantage of a native profiler built into the browser. Let’s look at that next. Figure 8.2 Mousemat example from chapter 4 with the JavaScript profiler running and generating a report on the active stopwatches. We have chosen to profile the window.onload event, the drawing of the thumbnail cursor in response to mouse movement, and the updating of the status bar with the mouse coordinates. count indicates the number of recordings made of each code block, and total the time spent in that block of code.138:T563,288 CHAPTER 8 Performance 8.2.2 Using the Venkman profiler The Mozilla family of browsers enjoys a rich set of plug-in extensions. One of the older, more established ones is the Venkman debugger, which can be used to step through JavaScript code line by line. We discuss Venkman’s debugging features in appendix A. For now, though, let’s look at one of i

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