1  <HTML>
  2  <HEAD>
  3  <TITLE>JavaScript Example:  Math Computation</TITLE>
  4  
  5  <SCRIPT LANGUAGE="JavaScript1.1">
  6  <!-- hide script from old browsers
  7  
  8  // Circle constructor:
  9  function Circle() {
 10    if ( arguments.length > 0 ) {
 11      this.r = Circle.arguments[0];
 12    } else {
 13      this.r = null;
 14    }
 15    this.getRadius = new Function( "return this.r" );
 16    this.setRadius = new Function( "r", "this.r = r" );
 17  }
 18  
 19  // Method to compute area of a circle:
 20  function Circle_area() {
 21    return Math.PI * this.r * this.r;
 22  }
 23  
 24  // Create a dummy Circle object:
 25  new Circle();
 26  
 27  // Add method to Circle object:
 28  Circle.prototype.area = Circle_area;
 29  
 30  // Compute area and update form:
 31  function areaOfCircle( form ) {
 32    var c = new Circle();
 33    c.setRadius( form.radius.value );
 34    form.output.value = c.area();
 35  }
 36  
 37  // end script hiding -->
 38  </SCRIPT>
 39  
 40  </HEAD>
 41  
 42  <BODY BGCOLOR="#FFFFFF">
 43  
 44  <H2>Mathematical Operations</H2>
 45  
 46  Demonstration of mathematical methods:<p>
 47  
 48  <FORM>
 49  
 50  Enter a value for the radius:<P>
 51  <INPUT TYPE="text" NAME="radius" VALUE = "10">
 52  <INPUT TYPE="button" VALUE="Find Area" 
 53         onClick="areaOfCircle(this.form)">
 54  
 55  <P>
 56  Area of a circle with this radius is
 57  <INPUT TYPE="text" NAME="output" SIZE=20>
 58  
 59  </FORM>
 60  
 61  <P> <HR> <P>
 62  
 63  Note:  The area of a circle with radius  r  
 64  is  PI * r^2 <P>
 65  
 66  </BODY>
 67  </HTML>