Question

Here is a little Javascript code snippet where I have used a function to simulate an object. I tried to reflect upon the member functions (which are really nested functions of the function) , but somehow the code does not work.

Can someone please help me understand why the code does not work. I am trying to understand the underlying principles of Javascript which cause this code to not work.

Thanks.

var test = function () {

    var first = function first () {
        alert ("first");
    }

    var second = function second () {
        alert ("second");
    }

};

function getOwnFunctions(obj) {
    for(var f in obj) {
        if(typeof(f) == "function" && obj.hasOwnProperty(f)) {
           alert(f);
        }
    }
}

getOwnFunctions(test);

Answer 1

A couple points here:

1. var defines the scope of the variable, which is saying that the
   first & second functions are
   only available inside the test
   function. To simulate a object,
   you want to use the this keyword.
2. for(var f in obj): the for loops
   over the object and returns the
   keys in obj, so typeof(f) will always return the type of the
   f variable which will be a
   string, you want to check for
   typeof(obj[f]]) which will return
   the type of the actual underlying
   property.
3. You want to call getOwnFunctions
   with a instance of test, not the
   actual test function:

.

var test = function () {    
    this.first = function() {
        alert ("first");
    }    
    this.second = function() {
        alert ("second");
    }    
};    
function getOwnFunctions(obj) {
    for(var f in obj) {
        if(typeof(obj[f]) == "function" && obj.hasOwnProperty(f)) {
           alert(f);
        }
    }
}

getOwnFunctions(new test);