Check for Function and Class Existence Using PHP
When you've inherited a big website or you're working on a group website where you don't have quick access to communicate with the other developers, it's important to not assume that a custom function or class name has not already been defined. Here's how you can protect yourself:
The PHP
if(!function_exists('show_article')) {
function show_article($id) {
//code here
}
}
if(!class_exists('my_class')) {
class myclass {
//code here
}
}
Using this type of programming can also protect you in case a file gets accidentally included twice. If a file with a function definition were to be included twice, you'd get an ugly "redefined" error when the function is realistically only in one file.
![Page Visibility API]()
One event that's always been lacking within the document is a signal for when the user is looking at a given tab, or another tab. When does the user switch off our site to look at something else? When do they come back?
![5 HTML5 APIs You Didn’t Know Existed]()
When you say or read "HTML5", you half expect exotic dancers and unicorns to walk into the room to the tune of "I'm Sexy and I Know It." Can you blame us though? We watched the fundamental APIs stagnate for so long that a basic feature...
![Introducing LazyLoad 2.0]()
While improvements in browsers means more cool APIs for us to play with, it also means we need to maintain existing code. With Firefox 4's release came news that my MooTools LazyLoad plugin was not intercepting image loading -- the images were loading regardless of...
![Create a 3D Animating Sidebar]()
Mozilla's Christian Heilmann is an evangelist that knows how to walk the walk as well as talk the talk. You'll often see him creating sweet demos on his blog or the awesome Mozilla Hacks blog. One of my favorite pieces...
It seems a little redundant to check for class existence when you’re trying to create a new class. If the class does exist, then you want yours to be named something else so that it can be used. I would personally want an error in the example above, so I knew to rename the class.
It would make sense to check for the class before instantiating it, but to check for the class before creating it, seems like it could create some confusing situations.
Thanks for this cool idea. Sometime it really becomes hard to follow other developers of the team, so this idea will really help.