Why isn't it possible to dynamically create a variable via self-invoking function in Javascript?

I'm trying to imita开发者_开发百科te some sort of constructor like in other programming languages. If I do it like this it doesn't work. :/ Sorry for being dumb! :/ Thanks for the help!!

  function foo(){

      this.makeVar = function(){this.newVar = 'hello world'}(); 

  }

 var test = new foo();
 alert(test.newVar); 

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Because you are calling the (anonymous) function directly, and not as a method on an object. So this is window.

Copy the value of this in the outside function to a variable that is still available on the inside function.

function foo(){
  var self = this;
  this.makeVar = function(){
    self.newVar = 'hello world';
  }(); 
}

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Don't apologise for "being dumb". Asking questions is actually smart (usually).

The function foo() already is a constructor, so there's no need for an internal constructor's constructor.