ISTQB Terminology – Understanding Defect in Testing

From this tutorial on efficient javascript:

One of the best kept secrets to boosting script performance is to cache your objects. Often times, your script will repeatedly access a certain object, as in the following demonstration:

<script type="text/javascript">
for (i=0;i<document.images.length;i++)
document.images[i].src="blank.gif"
</script>

In the above, the object "document.images" is what's accessed multiple times. The code to realizing it is inefficient, since the browser must dynamically look up "document.images" twice during each loop (once to see if i<document.images, and the other, to access and change the image's src). If you have 10 images on the page, for example, that's 20 calls to the Images object right there. Excessive calls to JavaScript objects can wear down the browser, not to mention your computer's memory.

The term "cache your object" means storing a repeatedly access object inside a user defined variable, and using that variable instead in subsequent references to the object. The performance improvement can be significant. Here's a modified version of the initial script using object caching:

<script type="text/javascript">
var theimages=document.images
for (i=0;i<theimages.length;i++)
theimages[i].src="blank.gif"
</script>

Not only is the number of times document.images[] is referenced cut in half with the above, but for each time it is referenced, the browser doesn't have to go through document.images first, but goes straight to its containing array.

Remember to use object caching when calling highly nested DHTML objects, like document.all.myobject, or document.layers.firstlayer etc.

and

some JavaScript objects are less forgiving on the browser than others. While recognizing exactly which isn't easy (and isn't the goal here), just becoming aware of this fact is important.

Take, for example, these two properties:

-object.innerText //IE only
-object.innerHTML

Did you know that the second property demands multiple times the system resources to call than the first? If all you're changing is the textual content of a <div> or <span> and in IE only, innerText would definitely be the more efficient choice. Another example are the CSS properties "display" and "visibility"; the former is significantly more expensive than the later.

With JavaScript object caching, the number of lookups is cutdown, since the object reference is held within the variable - potentially improving performance and memory usage.

The standard flow for TDD is:

1. Write a failing test. (Red)
2. Make the smallest code change that makes it pass (Green)
3. Refactor (Keeping it green)

The test for your tests in this case is step 1 - making sure that the test fails before you make any code changes.

Another test that I like is whether you can delete some code and re-implement it a different way, and your tests fail after deletion but work with a different algorithm in place.

As with all things, there is no magic bullet. Forgetting to write a required test is just as easy for a developer to do as forgetting to write the code. At least if you're doing both, you have twice as many opportunities to discover your omission.