Why does my Javascript snippet for a module return undefined on a private variable?

Question

I am struggling to see why my JS snippet is returning undefined in the console window...

var myModule = (function(){

  var _myVal;

  function _setMyVal(arg){

    _myVal = arg;

  }


  return {
    myVal : _myVal,
    setMyVal : _setMyVal
  };


}());

myModule.setMyVal("ss");

console.log(myModule.myVal);

Because setting myModule.myVal directly actually works!

myModule is an IIFE which has already been invoked, setting myVal to undefined — filur
– filur, Commented Nov 17, 2014 at 10:44

Scimonster · Accepted Answer · 2014-11-17 11:03:21Z

4

  return {
    myVal : _myVal,
    setMyVal : _setMyVal
  };

You are returning the current value of _myVal rather than a reference to it (which is what you want). After reassigning the variable _myVal in your function, myModule.myVal is still pointing to the old value.

If you want to return a reference, you can use a getter to return it:

  return {
    get myVal() {return _myVal},
    setMyVal : _setMyVal
  };

edited Nov 17, 2014 at 11:03

answered Nov 17, 2014 at 10:39

Scimonster

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1 Comment

Exitos Over a year ago

The answer is good although I'm not keen on the 'get' keyword I haven't seen it a lot and worry it will confuse people. I have refactored to two methods as it seems more orthogonal.... The getter buries the 'get' inside the inner function. getReferences : _getReferences, setReferences : _setReferences

lordvlad · Accepted Answer · 2014-11-17 10:42:08Z

0

That is just how JavaScript handles variables and object properties.

var x = 2;
var y = {x: x};   // at this point, y.x is set to the number two,
                  // it bears no reference to the variable x

console.log(x, y.x); // 2 2

x = 3

console.log(x, y.x); // 3 2

answered Nov 17, 2014 at 10:42

lordvlad

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