Object Inheritance Methods

This Javascript program demonstrates methods for inheriting a class of type. In the first example, the CRealNumber is extended by the CComplexNumber class. A class that is extended must create an instance of the base class when it instantiated. On the other hand, the prototype property allows us to inherit a specific instance of an object. The prototype is more confusing by more flexible. For example, a single object can be used as the prototype of a group of objects so that they can all share a base instance.

InheritanceMethods.html

<!DOCTYPE html>
<html>
<head>
    <title>XoaX.net's Javascript</title>
</head>
<body>
    <script type="text/javascript" src="InheritanceMethods.js"></script>
</body>
</html>

InheritanceMethods.js

// Start this here
class CRealNumber {
	constructor(dValue) {
		this.mdReal = dValue;
	}
	Magnitude() {
		return Math.abs(this.mdReal);
	}
}

class CComplexNumber extends CRealNumber {
	constructor(dReal, dImag) {
		super(dReal);
		this.mdImag = dImag;
	}
	Magnitude() {
		return Math.sqrt(this.mdReal*this.mdReal + this.mdImag*this.mdImag);
	}
}


function CVector2D(dX, dY) {
	this.mdY = dY;
	this.Magnitude = function () {
		return Math.sqrt(this.prototype.mdReal*this.prototype.mdReal + this.mdY*this.mdY);
	}
	this.prototype = new CRealNumber(dX);
}

var qVector3D = {
	mdZ : 4.0,
	Magnitude : function () {
		return Math.sqrt(this.prototype.prototype.mdReal*this.prototype.prototype.mdReal + 
			this.prototype.mdY*this.prototype.mdY + this.mdZ*this.mdZ);
	}
}

var qReal = new CRealNumber(3);
var qComplex = new CComplexNumber(-2, 1);
var qVector2D = new CVector2D(3.6, 2.3);
qVector3D.prototype = qVector2D;


document.write("<hr />");

PrintAnObject(qReal);
document.write("<hr />");
PrintAnObject(qComplex);
document.write("<hr />");
PrintAnObject(qVector2D);
PrintAnObject(qVector2D.prototype);
document.write("<hr />");
PrintAnObject(qVector3D);
PrintAnObject(qVector3D.prototype);
PrintAnObject(qVector3D.prototype.prototype);
document.write("<hr />");

document.writeln("Magnitude = " + qReal.Magnitude() + "<br />");
document.writeln("Magnitude = " + qComplex.Magnitude() + "<br />");
document.writeln("Magnitude = " + qVector2D.Magnitude() + "<br />");
document.writeln("Magnitude = " + qVector3D.Magnitude() + "<br />");


// This function just prints out the members of an object.
function PrintAnObject(qObject) {
  var iCount = 0;
  var sOutput = typeof(qObject)+": " + qObject.constructor.name + "<br />";
  for (var sProperty in qObject) {
    sOutput += "&nbsp;&nbsp;&nbsp;&nbsp;" + sProperty + ': ' + qObject[sProperty]+"<br />";
    ++iCount;
    if (iCount >= 15) {
      document.writeln(sOutput);
      document.writeln("&nbsp;&nbsp;&nbsp;&nbsp;...<br />");
      return;
    }
  }
  document.writeln(sOutput);
}