Does minified JavaScript code improve performance?
Minifying improves performance for your page overall by decreasing the load time (even if only slightly).
Neither minifying nor obfuscating alter the execution time by any perceivable amount for the vast majority of JavaScript code out there.
I do recommend minifying for those reasons and more. Minifying multiple scripts together (like jQuery and its plugins) can yield even greater savings.
As pointed out, on constrained devices and/or with very large codebases minifying could yield a noticeable result.
Minification
Minification does improve performance for two reasons:
-
Reduced file-size (because it removes comments and unnecessary white spaces), so your script loads faster. Even if it is embedded into the
<head>. -
It is parsed faster, since comments and white spaces don't have to be explicitly ignored (since they're not there).
Combining
I've written quite a few HTML/JavaScript AIR applications, and from personal experience, combining files won't make a difference. In fact, it's good practice to separate the script based on certain criteria (classes, global functions, SQL functions, etc.). It helps keep them organised when the project becomes too big.
Obfuscation
Obfuscating is usually a combination of minification and renaming variables. It involves using eval to blow up the code again. This reduces performance for obvious reasons, but it depends on the size of your code.
I'd suggest running tests to understand this best for your specific situation.
Everyone here already talked about minifying, but nobody talked about the second part of your question - combining. This will definitely improve performance, probably even more than minifying.
Multiple files require multiple HTTP requests, so when you put them all into one file, only one request is needed. This is important for two reasons:
- each individual HTTP request may take longer to load for various routing reasons, and one file will potentially delay your whole application.
- browsers and other clients have a maximum limit of files they are allowed to download concurrently from a single domain. Depending on the number of files in your application, this may mean the client queuing them up, thus making the load even longer.
Also, besides minifying and combining, you have to absolutely make sure you have some sort of server-side compression enabled. This can save you 90% or even more in the amount of bytes transferred, depending on the files.
You can read more about compression (gzip, deflate) in How to make your site lightning fast by compressing (deflate/gzip) your HTML, JavaScript, CSS, XML, etc. in Apache.