Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 5 ■ Presentation and Behavior (CSS and Event Handling)
The checkKey method determines whether window.event or the event object is in use and reads out the keyCode
in the appropriate manner:
keyChecking.js (excerpt)
checkKey:function(e){
if(window.event){
var key = window.event.keyCode;
} else if(e){
var key=e.keyCode;
}
It then retrieves the element (in this case via getElementById(), although you could as easily use
DOMhelp.getTarget(e), but why make it more complex than needed?) and checks whether the error property is
true. If it is true, there is already a visible error message and the Submit button is disabled. In this case, you need to
remove the error message, set the error property to false, and enable the Submit button (which is the next sibling of
the input element—use closestSibling() here to ensure it is the button and not a line break).
keyChecking.js (excerpt)
var v=document.getElementById('Voucher');
if(voucherCheck.error){
v.parentNode.removeChild(v.parentNode.lastChild);
voucherCheck.error=false;
DOMhelp.closestSibling(v,1).disabled='';
}
You determine that the key that was pressed is not any of the digits from 0 to 9—that is, that its ASCII code is not
between 48 and 57 inclusive.
■ ■Tip You can get the values of each key in any ASCII table, for example, at http://www.whatasciicode.com/.
If the key is not a number key, delete the last key entered from the field value and create a new error message.
Create a new span element, add the class, add the error message, append it as a new child to the parent of the text
entry box, and disable the form button. The last thing missing is to start voucherCheck.init() when the page has
finished loading.
keyChecking.js (excerpt)
if(key57){
v.value=v.value.substring(0,v.value.length-1);
voucherCheck.error=document.createElement('span');
DOMhelp.cssjs('add', voucherCheck.error, voucherCheck.errorClass);
var message = document.createTextNode(voucherCheck.errorMessage)
voucherCheck.error.appendChild(msg);
v.parentNode.appendChild(voucherCheck.error);
DOMhelp.closestSibling(v,1).disabled='disabled';
}
}
}
DOMhelp.addEvent(window, 'load', voucherCheck.init, false);
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