Archive for December, 2008

The difference between != and =!

Posted on December 31st, 2008 in JavaScript | No Comments »

I was helping a friend troubleshoot some of her code today and found the culprit to be a typo in one of her conditional statements:

// var USERID = 12345;
if (USERID =! null){
     // code

Her expression was always resolving to true because she had inverted her != (“not-null”) check which was actually assigning her variable to the return of a statement evaluation. Her mistake would be clearer to understand formatted as such:

// var USERID = 12345;
if (USERID = !null){
     // code

Since the inverse of false, null, and NaN is true her conditional statement (also an assignment) would always return true.

Which lead me to thinking, the not operator is a great way to write succinct code. In the right context, using the not operator in the right side of an assignment isn’t a bad idea.

Improve your jQuery – 25 excellent tips

Posted on December 16th, 2008 in JavaScript, jQuery | No Comments »

Here’s a nice write-up by Jon Hobbs-Smith at detailing 25 tips on using jQuery as well as regular JavaScript advice. Most of these tips probably aren’t anything new for the advanced jQuery user (Jon considers himself intermediate, I think that’s modest), however I love lists like this because there’s a treasure trove worth of experience being shared. Altruism at it’s best!

I plan on writing more entries on my own tips and tricks with JavaScript and jQuery as well as my methods of debugging in various browsers, compression techniques, etc., but in the meantime, I’ll just comment on Jon’s list:

2. Use a [jQuery] cheat sheet

I think Visual jQuery is all you need. And now that there’s live search and clickable examples it’s even better.

3. Combine all your scripts and minify them

Dead Edward’s packer is awesome for minifying, but before I do that, I like to run my code through jSlint to make sure it’s all valid. I ignore line-break errors as I don’t agree in many cases that it’s an issue.

Additionally, when I work on large JS codebases with a lot of other people who may not code as strictly as I do, I like to use JSmin on the minimal setting (cut-and-paste version here). The compression benefit is only slightly less and it preserves single linefeeds preventing JS errors where people forgot to end their statements with a semicolon. It also makes the code easier to read and debug in a production enviornment—great for the times you want the benefits of minification without the side effect of obfuscation.

5. Keep selection operations to a minimum by caching

I just wanted to comment in Ron’s example where he used:

var myList = $('.myList');

First, if I ever reference a jQuery collection in my scripts, I like to append the dollar sign character to the beginning of the variable name to signify that it is, in fact, a jQuery collection:

var $myList = $('.myList');

It’s a lot more helpful when you access that variable further down the road and don’t have to question whether it’s a jQuery wrapped set, an actual HTML element, or something else.

Secondly, whether you’re using a JS lib or not, I would never search for an HTML collection by class name alone; What the JavaScript engine is doing in the background is looping through every single element on the page which is very intensive. It would be better to find the closest parent container first or search by specific tag name(s):


var $myList = $('ul.myList'); //added benefit of knowing the type of element you'll
// receive


var $myList = $('#closest_parent_id .myList'); // searching the children of a parent
// container instead of all the elements on the page


var $myList = $('#closest_parent_id ul.myList'); // combination of both above

19. Use noconflict to rename the jquery object when using other frameworks
22. How to check if an element exists[...]

As I’ve probably mentioned before, I always like to use noConflict() in all my projects. I move jQuery to the $j namespace and save $ for a shorthand reference to document.getElementById – I think it’s what most js developers expect and if($('myDiv)) is a lot simpler to write out than if($('#myDiv).length !== 0) or even if($('#myDiv).length).

Thanks for the link Bryan!