The JavaScript Source: Forms : Bitmap/Object Script

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General

This script demonstrates the use of bitmasking to store values in a single variable and how to use objects with JavaScript.

Notes

Created by: Fernando Rios
Web Site: http://www15.brinkster.com/hxedit
Posted: November 3, 2007

Source Code

Paste this source code into the designated areas.

External file

Paste this code into an external JavaScript file named: bitmapObject.js

/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by: Fernando Rios | http://www15.brinkster.com/hxedit */
// These will be the bitmask values. They must be powers of 2
var ram128=1;
var ram256=2;
var ram512=4;
var cpu1000=64;
var cpu2000=128;
var cpu3000=256;
var hd20=2048;
var hd40=4096;
var hd80=8192;

// This will be our 'computer' object

function Computer (f){
  var features=f;//private variable of computer. stores the features

  /* Priviliged methods of computer. Can be accessed from the outside but 
    also has access to private variable 'features' */
  this.getFeatures=function(){
  var ret="";//return string

  /* This is where the bitmask operations occur.
  It will do a bitwise comparison of the features value with the
  value that were testing against. If the result is equal to the value
  were testing, the value was set. Remember to use a bitwise & instead of && */

  if((features & cpu1000) == cpu1000)
    ret+="CPU: 1Ghz\n";
  if((features & cpu2000) == cpu2000)
    ret+="CPU: 2Ghz\n";
  if((features & cpu3000) == cpu3000)
    ret+="CPU: 3Ghz\n";
  if((features & ram128) == ram128)
    ret+="RAM: 128MB\n";
  if((features & ram256) == ram256)
    ret+="RAM: 256MB\n";
  if((features & ram512) == ram512)
    ret+="RAM: 512MB\n";
  if((features & hd20) == hd20)
    ret+="HD : 20GB\n";
  if((features & hd40) == hd40)
    ret+="HD : 40GB\n";
  if((features & hd80) == hd80)
    ret+="HD : 80GB\n";
  return ret;
  	};

  this.setFeatures=function (feat){
    this.features=feat
 	};
}

Head

Paste this code into the HEAD section of your HTML document.


<script type="text/javascript" src="bitmapObject.js"></script>

Body

Paste this code into the BODY section of your HTML document


<form name="theForm">
Select desired features<br>
CPU:
<select style="width=125" name="cboCPU">
  <option value=64>1Ghz (1000Mhz)</option>
  <option value=128>2Ghz (2000Mhz)</option>
  <option value=256>3Ghz (3000Mhz)</option>
</select><br>
RAM:
<select style="width=125" name="cboRAM">
  <option value=1>128MB</option>
  <option value=2>256MB</option>
  <option value=4>512MB</option>
</select><br>
HD:   
<select style="width=125" name="cboHD">
  <option value=2048>20GB</option>
  <option value=4096>40GB</option>
  <option value=8192>80GB</option>
</select><br>

<!--remember to use | (bitwise OR) when setting the bitmask-->
<input type="button" value="1. Set Attributes" onclick="Javascript:aComputer=new Computer(cboCPU.options[cboCPU.selectedIndex].value | cboRAM.options[cboRAM.selectedIndex].value | cboHD.options[cboHD.selectedIndex].value);">
<input type="button" value="2. Get Attributes" onclick="Javascript:alert(aComputer.getFeatures());")<br>
<input type="reset" value="3. Reset">
</form>

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