Question

I wrote the following class in javascript

function main() 
{
  this.area ;
  this.$= function(target)
  {
    if(target == undefined)
    {
      this.area = document;
    }
    else
    {  
      this.area = document.getElementById(target);
      if( this.area == null )
      {
        this.area = document.getElementsByTagName(target);
        if( this.area[0] == null )
        alert("Error value "+target+" passed to $() is no an id or name");//code to create variable
      }
    }
  }
  this.display = function(value)
    {
      if(this.area == undefined)
      alert("Error in display() method...target not selectedddd");
      else area.innerHTML = value;
    }
}
    and i always get the error message I given as alert. Why area is always null? 

If I refer to area without using the this keyword will it work. Is there any way to nest classes in javascript like

function()
{
  this.a;
  function()
  {
  }
}

Answer 1

The reason why it does not work is that this refers to the inner function scope, not the outer function scope you call a “class”.

Try something like this instead:

function MyClass() {
    // This is the constructor.
}

MyClass.prototype = {
    method: function() {
    },

    foo: function() {
    }
};

var instance = new MyClasss();
instance.method();