If you are writing a lot of jQuery you’ll likely have files with loads of JavaScript functions and variables that may be completely independent and shouldn’t interfere with each other.
If you have a lot of this going on (or even if you don’t) you might consider wrapping up related variables & functions using closures that run immediately. These are also known as Immediately Invoked Function Expressions (IIFE) and are a fantastic approach to encapsulating your JavaScript.
In the example above, our IIFE is invoked immediately and encapsulates references to the jQuery, window, and document objects by passing them into the function.
You’ll also notice that the function accepts the undefined argument with isn’t passed in when invoked.
This is just an added bonus as it simplifies undefined checks which can be a little finicky in JavaScript. By including the argument as per the snippet, you can simply check if a variable is defined using myvar !== undefined.
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