Possible issue when omitting semi-colons in JavaScript

In my latest JavaScript projects I’ve tried to omit the semi-colon (;) on line endings. Why? I don’t know, because I can? I’m not going to go into a deep discussion about this subject here but rather warn others who follows this practice. I do have a solution at the end though so don’t give up just yet!

The following code (in Firefox 21.0) yields a null is not a function error message in Firebug.

var foo = null

(function($) {
	// Do something
})(jQuery)

Notice the lack of a semi-colon when defining the variable “foo”.

The following code parses just fine:

var foo = null;

(function($) {
	// Do something
})(jQuery)

Apparently the parser believes I’ attempting to run null as a function, ergo it thinks I want to do this:

var foo = null(function($) {
	// Do something
})(jQuery)

Solution

What I suggest is to always start a closure with a semi-colon (as seen in the code below). This guarantees that you won’t run into this issue in the future. Of course, if you always end statements with semi-colons then nevermind..

var foo = null

;(function($) {
  // Yay, it's working
})(jQuery)

Happy coding 🙂