Question

I came across this unique practice in a browser detection script.

if (/MSIE/.test(_3)) {
    IE = true;
} else {
    if (/AppleWebKit/.test(_3)) {
        Safari = true;
    } else {
        if (/Opera/.test(_3)) {
            Opera = true;
        } else {
            if (/Camino/.test(_3)) {
                Camino = true;
            } else {
                if (/Firefox/.test(_3) || /Netscape/.test(_3) || ) {
                    Mozilla = true;
                }
            }
        }
    }
}

Are there any advantages to using this nested If/Else method?

What if I just changed it to:

 if (){
 } else if (){
 } else if (){
 } else if (){
 }

Would it run slower or anything?

Answer 1

In this case the switch statement could also be used? Something like:

switch ((_3).match(/msie|applewebkit|opera|camino|firefox/i)[0]) {
  case 'MSIE' : /* ...; */ break;
  case 'AppleWebKit' : /* ...; */ break;
  /* ... etc. */
  default: BrowserCouldntBeDetermined = true;
}

I adhere to the previous answer: else if() is equivalent to but more readable then else { if () …}

Anyway, the code you found and presented looks a bit clumsy and not really fast for other reasons than the way if...else is used. Concerning the meaning of the code (and aside from the question), a better way to take care of browser differences is by object detection I would say.