// --------------------------------------------------
//    Creating an object with methods

function mycircle(x,y,r) {
  this.xcoord = x;
  this.ycoord = y;
  this.radius = r;
  this.retArea = getTheArea;
  //This next line uses an alternative syntax
  this.retCirc = function () { return ( Math.PI * this.radius * 2 ); };
  this.mvBy = mvCclBy;
}
function getTheArea() {
  return ( Math.PI * this.radius * this.radius );
}
function mvCclBy(xDis,yDis) {
  this.xcoord += xDis;
  this.ycoord += yDis;
}

/*
create a mycircle called testcircle where testcircle.xcoord is 3
and testcircle.ycoord is 4 and testcircle.radius is 5
*/
var testcircle = new mycircle(3,4,5);
/*
use the mvBy method to displace the centre of testcircle.
move it by 2 in the x direction and 3 in the y direction
*/
testcircle.mvBy(2,3);
//testcircle.xcoord is now 5 and testcircle.ycoord is now 7

window.alert( 'The area of the circle is ' + testcircle.retArea() );
window.alert( 'The circumference is ' + testcircle.retCirc() );


// --------------------------------------------------
//    Advanced object techniques

testcircle.texture = 'smooth';
mycircle.prototype.texture = 'smooth';  
// all of the mycircles that we have created will now inherit the new property:

alert(testcircle.texture);
//alerts 'smooth'

mycircle.prototype.setArea = function (oArea) {
  this.radius = Math.sqrt( oArea / Math.PI );
};
mycircle.setArea(5);


function mycircle(x,y,r) {
  this.xcoord = x;
  this.ycoord = y;
  this.radius = r;
}
mycircle.prototype.retArea = function () {
  return ( Math.PI * this.radius * this.radius );
};
mycircle.prototype.retCirc = function () {
  return ( Math.PI * this.radius * 2 );
};
mycircle.prototype.mvBy = function (xDis,yDis) {
  this.xcoord += xDis;
  this.ycoord += yDis;
};


// --------------------------------------------------
//    Sub-classes and class inheritance

/*
This effectively makes mysphere a sub-class of mycircle, and making the mysphere class constructor inherit from the mycircle class constructor is as simple as this:
*/
function mysphere(x,y,z,r) { ... constructor code ... }
mysphere.prototype = new mycircle();

------------

function mycircle(x,y,r) {
  if( arguments.length ) { this.getready(x,y,r); }
}
mycircle.prototype.getready = function (a,b,c) {
  this.xcoord = a;
  this.ycoord = b;
  this.radius = c;
};
mycircle.prototype.retArea = function () {
  return ( Math.PI * this.radius * this.radius );
};
mycircle.prototype.retCirc = function () {
  return ( Math.PI * this.radius * 2 );
};
mycircle.prototype.mvBy = function (xDis,yDis) {
  this.xcoord += xDis; this.ycoord += yDis;
};

-------

function mysphere(x,y,z,r) {
  if( arguments.length ) { this.getready(x,y,z,r); }
}
//inherit from the mycircle prototype
mysphere.prototype = new mycircle();
//put the correct constructor reference back (not essential)
mysphere.prototype.constructor = mysphere;

mysphere.prototype.getready = function (a,b,c,d) {
  //reference the getready method from the parent class
  this.tempReady = mycircle.prototype.getready;
  //and run it as if it were part of this object
  this.tempReady(a,b,d);
  //now that all required properties have been inherited
  //from the parent class, define extra ones from this class
  this.zcoord = c;
}
mysphere.prototype.mvBy = function (xDis,yDis,zDis) {
  //override the existing method
  this.xcoord += xDis;
  this.ycoord += yDis;
  this.zcoord += zDis;
};
mysphere.prototype.retVol = function () {
  return ( 4 / 3 ) * Math.PI * Math.pow( this.radius, 3 );
};
mysphere.prototype.retSurf = function () {
  return 4 * Math.PI * this.radius * this.radius;
};

--------

//  to use it
var testsphere = new mysphere(3,4,5,6);

alert( 'The cross-section area is ' + testsphere.retArea() );
alert( 'The circumference is ' + testsphere.retCirc() );
alert( 'The volume is ' + testsphere.retVol() );
alert( 'The surface area is ' + testsphere.retSurf() );

http://www.howtocreate.co.uk/tutorials/javascript/objects">creating objects

Creating objects

object

JavaScript