Question

I’m writing a function add_event as the following shows:

function add_event(o, event_type, callback, capture){
    o = typeof o === "string" ? document.getElementById(o) : o;
    if(document.addEventListener){
        add_event = function(o, event_type, callback, capture){
            o = typeof o === "string" ? document.getElementById(o) : o;
            o.addEventListener(event_type, callback, capture);
        }
    }else if(document.attachEvent){
        add_event = function(o, event_type, callback, capture){
            o = typeof o === "string" ? document.getElementById(o) : o;
            o.attachEvent("on" + event_type, callback);
        }
    }
    add_event(o, event_type, callback, capture);
}

Now my question is whether the statement

o = typeof o === "string" ? document.getElementById(o) : o;

affects the performance of this program? If you pass an HTML element instead of an id, you infact executes the statement o = o, this is the reason why I ask this question. Great Thanks.

Answer 1

Chances are that the js interpreter will optimize it out. Even if it doesn’t, the effect won’t be noticeable. And if you’re really concerned, change it to:

if(typeof o === "string")
  o = document.getElementById(o);