JavaScript is an extremely powerful and flexible scripting language. Unfortunately flexible, for many people, means fallible. I am going to highlight 5 best practices that you can use in any JavaScript project. These are very broad, I will follow up soon with more specific best practices.

First and foremost, keep your code simple, clean and well documented. This is by no means unique to JavaScript but many people seem to think it is the exception to the rule. Your code should naturally comment itself but it is also important to at least introduce every function. I recommend two versions, a fully documented and formatted version and then a compressed version that you use in production. There are a number of free online utilities that can strip out comments and pack your script. There is no need to push out the extra size required for the documentation and formatting.

Second, keep your JavaScript in an external file. The only exception to this rule is if you have some very lightweight script specific to a single page or are setting up variables that cannot be done in the external JS. An external file results in greater scalability, maintainability and degradability. The correct way to reference an external JS file is as follows:

<script type="text/javascript" src="script.js"></script>

Third, separate your JavaScript from the presentation layer. We have all heard of unobtrusive JavaScript but we still see inline script all the time. Instead of cluttering your font-end code with dozens of event handlers add them dynamically. There are exceptions to this rule so please use common sense and separate the layers when it makes sense. An example of adding an onclick event handler from JavaScript:

var div = document.getElementById('div');
div.onclick = new Function("processClick(this)");

Fourth, properly define and scope variables. Many of the scripts I download hoping to use in a project I immediately throw out. The reason being that the programmer did not take the time to properly define and scope variables. Always reference the first instance of a variable by using var. Otherwise the only way someone can know if that is the first reference to that variable is by starting at the top and reading all the way down. It is also important to scope variables correctly. Don’t scope a variable on the global level unless you need it there. I also recommend differentiation of global and local variables though some kind of visual identifier such is all caps on global variables or some easily identifiable character.

Fifth, don’t assume JavaScript support in the first place. Depending on your audience you may choose to disregard this suggestion but for mainstream websites I highly suggest coding with the minority in mind (an estimated 5-10% of web users do not have JavaScript enabled) and degrade your scripts gracefully. JavaScript should be considered as an added feature and not a dependency. An examples of this would be links, the most fundamental element of a web page.

<a href="javascript:processClick()">link</a>
<a href="#" onclick="javascript:processClick()">link</a>


If the user clicks the either of the links above with JavaScript disabled nothing will happen. However, with the code below they could still navigate.

<a href="link.html" onclick="processClick(); return false;">link</a>