findItem.js

var findItem = function(jid, items){
    for(var i = 0; i < items.length; ++i){
        var item = items[i];
        if(item.jid === jid){
            return item;
        }
    }
    return null;
}

findItem_some.js

var findItem = function(jid, items){
    var foundItem = null;
    dojo.some(items, function(item){
        return (item.jid === jid) ? (foundItem = item, true) : false;
    });
    return foundItem;
}

Won't work, that's where I tripped to initially. The return form will return from the inner function only, not from findItem.

//oh sorry that was a stupid typo, forgot a return. programming in ruby has made me forget to return :)
//is this better?

var findItem = function(items, jid) {
   return items.filter(function(item) {return item.jid === jid})[0]
}

Yep, this works. Returns undefined instead of null (atleast in Chrome), but that's not a big deal.

Ruby doesn't need explicit returns? That's cool! Lisp doesn't need explicit returns either, that's where I made a lot of mistakes when I started working with javascript.

yeah ruby returns the last expression evaluated. return is used explicitly only in guard clauses :)

I just realized one issue with your snippet: it doesn't return as soon as it finds a match, rather it always goes through the entire array. The original snippets that I posted, on the other hand, quit as soon as they find a match.

Given this, can we do any better?

var arrayFind = function(items, predicate) {
for (int i=0; i<= itens.length; i++) {
if predicate(items[i], i) return items[i];
}
}

and then the rest is obvious

Haha, you've just implemented Common Lisp's some; I was wondering if there was a more concise solution apart from writing some in JS. If Javascript's Array.some behaved like this rather than returning just a boolean, it would have been so much more useful.

oh, yeah some is pretty neat in that it returns the value. I like that. Ruby's array.find does this, that's why I called it find. There is also an "any" which is meant to be used like some. Except you can rely on it even if your array contains false or nil ;-)