miscoded

I guess Finnair is the household's favourite airline. I don't think I've used any other carrier during the last three years or so - we don't travel that much, so we're not talking many flights overall. However, it was rather annoying to find its website broken last time I wanted to look up some prices:

Finnair site auto-complete menu broken, error in console

After selecting a local site, the auto-complete menu to choose departure and destination cities from never populates. What's worse: the site doesn't accept anything you type in by hand! If you haven't made a menu selection, you get an error message! I'm sure that does wonders for their overall accessibility and section 508 compliance..

The error message complains that they refer to a variable "i" that doesn't exist. Somewhat wrapped, the code looks like this:

a.Autocompleter.Cache=function(c){
	var f={};
	var d=0;
	function h(k,j){
		if(!c.matchCase){
			k=k.toLowerCase();
		}
		if(!k.startsWith(j)&&k.indexOf(" "+j)===-1&&k.indexOf("("+j)===-1){
			return false;
		}
		return i==0||c.matchContains;
	}

The problem is the reference to i in the return statement. There is no variable "i" defined nearby, indeed not in the entire script file. That "i==0" looks like some dead code that isn't meant to be there anymore. But it works in other browsers, no?

If I load the page in Firefox and type javascript:alert(window.i) into the address bar it says "1", so in Firefox the site does somewhere create a global variable named i. The question is where?

Firebug can't - as far as I know - break when a variable is initialized or changed. As always, Fiddler comes to the rescue - setting a "HTTP breakpoint" after response and re-loading the site in Firefox lets me add some simple debug code:
Fiddler screen in breakpoint mode, debug code highlighted

window.__defineSetter__ ('i', function(){ try{ undefined() ; }catch(e){ console.log(e) ; } })

When I click Fiddler's "run to completion" button, an error message appears in Firebug's console pointing to this function:

function isFirefoxWMPPluginInstalled(){
	var plugs=navigator.plugins;
	for(i=0;
	i<plugs.length;
	i++){

which given its name is naturally called after some browser sniffing, here:

type:$.browser.mozilla&&isFirefoxWMPPluginInstalled()?"application/x-ms-wmp":"application/x-mplayer2"

So this works in other browsers by pure luck - because JavaScript scoping rules are such that when you don't use "var" keyword to declare variables, they will be global, and Fnnar's code contains numerous loops that use "i" as a counter and don't use var. If such a loop happens to run before you try booking, the site will work for you. As if we needed any more evidence that JavaScript scoping rules suck..

If we're going to site patch this error in browser.js, the patch would be simply var i;. At 6 characters, I'm fairly sure it would be the shortest site patch ever. Meanwhile, we'll contact them and hope Fnnar will get their "i"s back in order.

And I sure hope they deploy better software for their autopilot than their autocomplete...