I'm playing around with different design patterns in Javascript. This factory has got me confused

I'm playing around with different JS design patterns, and im trying to modify some samples I've seen out there. I saw an example of a xhr开发者_JAVA百科 factory, that had several nested try/catch statements that were nested within eachother.

try{
...
}catch(e){
    try{
    ...
    }catch(e){}
}

I figured I'd be able to do a self-invoking function. However It seems to have eluded me as to how it should work. Does anyone have any advice?

Example:

http://jsfiddle.net/jiggliemon/a7xWq/2/

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[Update]:

http://jsfiddle.net/jiggliemon/b5LaZ/embedded/

Case Closed.

---

Changed try loop to:

for(var i = 0, l = instances.length; i < l; i ++) {
    try{
        var obj = instances[i].getInstance();
        return instances[i];
    }catch(e){ }
}

Full code

---

var XHR = (function(){
    var ins = [
        function(){return new XMLHttpRequest();},
        function(){return new ActiveXObject('Msxml2.XMLHTTP');},
        function(){return new ActiveXObject('Microsoft.XMLHTTP');}
    ],i,tmp;

    return (function tryIns(i){
        i = i || 0;
        while(i < ins.length){
            try{tmp = ins[i]();}
            catch(e){i++; tryIns(i);}
            finally{return ins[i];}
        }
        throw new Error("Your browser doesn\'t support Ajax requests");
    })();
})();