So, after a reasonably successful "Tips for Faster PHP Scripts" series, I've thought about what else I could write about. As I've been using JavaScript quite a lot recently, I decided to write about ways to improve scripts so they run faster.

It is important than JavaScript scripts are fast, because you can not determine the execution speed on the wide range of clients' browsers.

You can not also determine how fast peoples' internet connections are, so it is important that the scripts get to the clients' browsers as fast as possible.

Some of these tips may not be entirely practical and may make the scripts harder to maintain, but I believe there should be compromise between making maintainable code and speed- and resource- efficient code.

1. Combining Scripts to One File

When Javascript files are requested, the server sends a few headers. Sometimes these headers can take more bytes than actual JavaScript itself.

For example, if 5 single JavaScript files are requested, they each will be received like this (with headers shown):

HTTP/1.1 200 OK
Date: Sat, 16 Feb 2008 18:55:10 GMT
Server: Apache/2.2.4 (Win32) mod_ssl/2.2.3 OpenSSL/0.9.8d PHP/5.2.1
Last-Modified: Sat, 16 Feb 2008 18:55:08 GMT
ETag: "6d37-86-fd04022"
Accept-Ranges: bytes
Content-Length: 134
Connection: close
Content-Type: application/x-javascript

function aFunctionName(arg1, arg2) {
if(arg1 == arg2)
return 0;
if(arg1 < arg2)
return -1;
if(arg1 > arg2)
return 2;
}

The total size of this transmission, including headers, is 424 bytes. The code itself is just 125 bytes. If similar code was loaded 5 times, the total size of the transmissions will be 2120 bytes. If, though, all the code was put into one file, the size of transmission would be 933 bytes, a saving of about 56%.
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