What happens with “var” variables inside a JavaScript Constructor?

Question

example:

function Foo() {
    this.bla = 1;
    var blabla = 10;
    blablabla = 100;
    this.getBlabla = function () { 
        return blabla; // exposes b         


        

Answer 1

In your example blabla is a local variable, so it will go away when the constructor function ends.

If you declare a function inside the constructor, which uses the variable, then the variable will be part of the closure for that function, and survives as long as the function (i.e. normally as long as the object):

function Foo() {
  this.bla = 1;
  var blabla = 10;

  this.getBlabla = function() {
    alert(blabla); // still here
  }
}