Is there any way to make this JavaScript tab completion script more efficient?

Question

This code is to be integrated into an AJAX Chat system to enable a tab auto-completion of user names:

var usernames = new Array();
usernames[0] = "Saladin";
usernames[1] = "Jyllaby";
usernames[2] = "CadaverKindler";
usernames[3] = "qbsuperstar03";

var text = "Text and something else q";

// Start of the script to be imported
var searchTerm = text.slice(text.lastIndexOf(" ") + 1);
var i;
for(i = 0; i < usernames.length && usernames[i].substr(0,searchTerm.length) != searchTerm; i++);
// End of the script to be imported

document.write(usernames[i]);

A couple of notes to be made: The array of usernames and the text variable would both be loaded from the chat itself via AJAX (which, unfortunately, I don't know), and the final output will be handled by AJAX as well.

Is there a more efficient way to do this?

Also, any tips on how to handle multiple instances of the searchTerm being found?

Answer 1

You can make this significantly more efficient (provided large number of users) by keeping the array sorted and using binary search to find the match.

Answer 2

The way you have it coded now:

for(i = 0; i < usernames.length && usernames[i].substr(0,searchTerm.length) != searchTerm; i++);

You are checking the length of usernames and the length of searchTerm as well as getting a substr from usernames[i] EVERY time the loop uh, loops.

For any of these that you don't expect to change during the course of the loop, you should store them in a variable before the loop starts.

Getting a value out of a variable is much faster than checking an object property or method.

So something like:

for(i = 0,ii=usernames.length,j=searchTerm.length; i < ii && usernames[i].substr(0,j) != searchTerm; i++);

Answer 3

Micro-optimization: instead of getting the substring and comparing it (creating lots of temporary strings)...

usernames[i].substr(0,searchTerm.length) != searchTerm

...you should use indexOf, which creates no temporary strings...

usernames[i].indexOf(searchTerm) == 0

What do you mean by "multiple instances of the searchTerm being found"? Can you give an example of the problem you're thinking of?