Question

I’ve been trying to see if I can build my JavaScript objects as intuitively as possible while making sure it’s as ‘correct’ as possible. I’ve been running a bunch of different scenarios through Crockford’s JSLint.com and haven’t had much luck. I seem to fix one error, then another pops up because of the change. Below is about as good as I can get. Anyone have another take on this?

This is a typical way I structure an object:

function gizmo(id) {

  /* private variables */

  var myId = id;

  /* private methods */

  var init = function () {
    if (myId < 1) {
      setId(1);
    }
  };

  var setId = function (newId) {
    myId = newId;
  };

  // run 'constructor'
  init();

  /* public methods */

  return {
    getId: function () {
      return myId;
    },
    setId: function (newId) {
      setId(newId);
    },
    incrementId: function (inc) {
      setId(myId + inc);
    }
  };
}

// creating an instance of gizmo

var myGizmo = gizmo(-2);
console.log(myGizmo.getId()); // outputs 1

myGizmo.setId(5);
console.log(myGizmo.getId()); // outputs 5

myGizmo.incrementId(2);
console.log(myGizmo.getId()); /// outputs 7

This seems to work well. However, when I run this through JSLint, it gives me an error stating that my two private functions are ‘Implied Globals.’

The best I can come up with is to declare my functions at the top with the variables like this:

function gizmo(id) {

  /* private variables */

  var myId = id,
      init,
      setId;

  /* private methods */

  init = function () {
    if (myId < 1) {
      setId(1);
    }
  };

  setId = function (newId) {
    myId = newId;
  };

  // run 'constructor'
  init();

  /* public methods */

  return {
    getId: function () {
      return myId;
    },
    setId: function (newId) {
      setId(newId);
    },
    incrementId: function (inc) {
      setId(myId + inc);
    }
  };
}

Answer 1

I’m pretty sure it’s a bug in JSLint. It hasn’t seen setId yet, so it assumes it’s global. But in reality, it makes no difference, because all vars are hoisted, per ECMAScript 5 10.5. This means your first example and the second are the same semantically. A local variable declaration anywhere in the function is processed immediately, and the binding is initially set to have undefined value. But by the time the function (e.g. init) actually runs, the closed-in value is no longer undefined.

To see that setId is initially undefined, but never refers to a global, do this test:

function setId()
{
  alert("Global setId");
}
function f()
{
  var init = function()
  {
    setId();
  }
  alert(typeof(setId));
  init();
  var setId = function()
  {

  }
}

It will alert undefined, then throw a TypeError error.