Question

This is a follow-up to my previous query. I have been trying some code since then :

var myFunc = function(){
    this.int1=1;
    var int2=2;
};
myFunc.int1=3;
myFunc.int3=4;

for(var name in myFunc){
    console.log('myFunc...'+name+'='+myFunc[name]);
};

var myFuncImpl = new myFunc();
myFuncImpl.int1=5;
for(var name in myFuncImpl){
    console.log('myFuncImpl...'+name+'='+myFuncImpl[name]);
};

And I get output as :

myFunc...int1=3
myFunc...int3=4
myFuncImpl...int1=5

I can’t answer the following questions :

1. Why isn’t int2 visible as a property to myFunc ? It’s still in myFunc’s scope, right ? Where does this definition disappear ?

2. Why I am I able to over-write int1‘s value outside function scope ? What if someone accidentally deletes my values outside code ? For “objects”, I understand “Object.freeze()” can help over myFuncImpl – but what about function definitions like myFunc ?

3. Why can’t I access int3 from myFuncImpl ? Where did the prior definition (while defining myFunc) go ?

I guess my doubts are due to my thinking of myFunc as a “class” (as in Java) and myFuncImpl as an object. Perhaps I am straying too far ?

Thanks !

Answer 1

1. int2 is effectively a private variable, so code outside the function cannot detect it http://javascript.crockford.com/private.html

2. This is just a fact of life with “vanilla” JS. if you need to prevent overwriting values, implement with Object.defineProperty. Caveats with IE<9

3. int3 is a ‘static’ property to the function. It is not available on the instance, sort of like in C# if you have a static method, it’s not available to instances of the class. The difference here is you can later on in your code say myFunc.int1 = "asdf"; and now your ‘static’ property has changed. Don’t confuse static with constant
   http://elegantcode.com/2011/01/19/basic-javascript-part-7-static-properties-and-methods/