Question

http://jsfiddle.net/ZLH7J/1/

What the jsFiddle and code below shows are two examples that essentially do the same thing. When trying to call first(); or this.first(); in either example, an undefined error is thrown. I can call the functions later through the instance, but not when trying to instantiate the object using init(){...}() like a constructor. I put init() at the bottom thinking it was an order of operations thing, but that is not the case. This does not work the way I thought it would work.

I am curious to understand how this is supposed to be done, and why this cannot be done.

//create and return an obj
var fishSticks = function(){
    return {
        first: function(){
            document.getElementById('output').innerHTML="Success";
        },
        init: function(){
            try{
                first(); //err
                this.first(); // also err
             }catch(e){
                document.getElementById('output').innerHTML=e.toString();
            }
        }()
    }
}   

//do function stuff and then return 'this'
var fishFillet = function(){
    var first = function(){
            document.getElementById('output2').innerHTML="Success";
    }
    var init = function(){
            try{
                first(); //err
                this.first(); // also err
             }catch(e){
                 document.getElementById('output2').innerHTML=e.toString();
            }
    }()
return this;
}

 var test = new fishSticks();    
 var test2 = new fishFillet();

​

Answer 1

You need to understand two things:

1) JavaScript does not automatically insert this like Java does, so the first() call will only look through the lexical scope for a definition of first, it will nok look at the this object. Therefore the call to first() should work but this will be bound to something else than what you might expect inside first.

2) Local variables in a constructor do not become members of the constructed object.