Javascript object declaration

Question

I'm building a library that is a loading screen which allows me to call Loader.Show(), Loader.Hide() or Loader.Step() from various different documents.

I've built the library, however I do not fully understand the various ways to declare objects. Whats the difference in the following two models, and which is better?

//Example 1
var Robot = (function () {
	var metal = "Steel";
  
  return {
    killAllHumans: function() {
        alert(metal);
    }
  }
})();
Robot.killAllHumans();

//Example 2
var NonRobot = {
  runState: "Normal",
  run: function() {
  	alert(this.runState);
  }
}
NonRobot.run();

I understand that both example 1 & create objects. I also understand that in Example 1, metal is a private variable. I do not know how to create a private variable in example 2. Is the only difference the scope?

Answer 1

This method creates a private context where you could add your own variable and do some intermediate evalations or even create private variables, such as metal

var Robot = (function () {
    var metal = "Steel";

  return {
    killAllHumans: function() {
        alert(metal);
    }
  }
})();

On the other hand, this version creates is an object literal:

var NonRobot = {
  runState: "Normal",
  run: function() {
    alert(this.runState);
  }
}
NonRobot.run();

runState is not a private property of NonRobot and it can be manipulated by outside forces.

Answer 2

In the first instance you are using an Immediately Invoked Function Expression as a constructor.

In the second, you are creating an object using an object literal.