Question: Where do you assign methods to an object? In Constructor or Prototype?

Before learning this, you need to understand about closure. Closure is a function which shares the lexical scope of outer function, hence it keeps hold on the memory even when outer function is resolved.

Now Consider the following case

function MyObject(name, message) {
  this.name = name.toString();
  this.message = message.toString();
  this.getName = function() {
    return this.name;
  };

  this.getMessage = function() {
    return this.message;
  };

}

So whenever call the constructor of MyObject, these functions get reassigned which is not memory efficient.

var obj = new MyObject('abc', 'Sample Message');

So it is better add methods to the prototype, unless you specifically need to create closures where both functions needs to share the same lexical environment.

function MyObject(name, message) {
  this.name = name.toString();
  this.message = message.toString();
}
MyObject.prototype = {
  getName: function() {
    return this.name;
  },
  getMessage: function() {
    return this.message;
  }

};

In following example, it is better to add inside constructor

function MyObject(name, message) {
  _counter = 0;
  this.message = message.toString();
  this.getCounter = function() {
    return this._counter;
  };

  this.setCounter = function(value) {
    this._counter = value;
  };

}

In above example, we are creating a private variable which is getting exposed to outer environment through getters and setters). Since both functions needs to share the same scope, we have added them inside constructor.