Question

function Peon(number) {
  this.number = number;

  this.inc = function() {
    number = number + 1;
  };

  return true;
}
var p = new Peon(10);

function returnNumber() {
  p.inc();
  alert(p.number);
}

<input id="b00" type="button" value="Click" onclick="returnNumber()">

This code doesn’t work as intended. Is there a way to make it work without having to write

this.number=this.number+1;

Here it is a trivial choice, but in bigger codes not having this.* would make it a lot more readable. Is it possible?

Answer 1

You can make number "private", but then you need a getter:

function Peon(number) {
  var number = number;

  // increment
  this.inc = function() {
    number++;
  };

  // a simple getter
  this.getNumber = function() {
    return number;
  }
}

var p = new Peon(10);

function returnNumber() {
  p.inc();
  alert(p.getNumber());
}

<input id="b00" type="button" value="Click" onclick="returnNumber()">

You should read Douglas Crockfords "The Good Parts" for more information on how to use this pattern, there’s (limited) a preview available at Google Books.

Also you don’t need to return something from the constructor, your return true is superfluous.