Javascript class without framework

function my_class(parameter1){
   this.variable1 = null;
   this.variable2 = null;

   this.constructor = function(){
     this.variable1= parameter1;
     this.echo();
   }

   this.echo = function(){
     alert(this.variable1);
   }

   return this.constructor();
}

var instance = new my_class(parameter1);