oop - How to extend a class in JavaScript -

i'm working on chess game built in javascript. i'm taking object-oriented approach , having difficulty working javascript's inheritance. want there "piece" abstract class holds fields , basic getters/setters such piece black or white. want have classes each type of piece can instantiate so:

var pieceone = new pawn(); 

the pawn() should have fields , methods of piece have own method movement, , additional fields (such whether or not has moved yet, doesn't matter pieces). here's current piece class:

//this object specifies basic information pieces. "use strict"; function piece(color, type, captured, hasmoved) {         this.color = color;     this.type = type;     this.captured = captured;     this.hasmoved = hasmoved;     this.image = color + "_" + type + ".svg"; } piece.prototype.getimage = function getimage(){     return this.image; } piece.prototype.iscaptured = function iscaptured(){     return this.captured; }; 

i know if going make subclass every kind of piece i'd eliminate "type" field, how make pawn subclass? this?

function pawn() = new piece(color, captured, hasmoved); pawn.prototype.getlegalmoves = function getlegalmoves(){     //return legal moves } var pieceone = new pawn("black", false, false); 

if willing take object oriented approach on js recommend follow power constructor pattern.

basically have function creates objects , take advantage of closures hide internal properties (fields or methods).

 function myobject(){     var that={};     var myprivatefield;     var myprivatefunction=function(){     }      that.mypublicmethod=function(){      }     return that;      } 

then can call method myobject() , new object of type.

you can extend example use inheritance calling power constructor of object , use object augmentation. take @ example of parasatic inheritance of douglas crockford.