[Claus Mygind]

with the "onKeyPress" event handler I see that I can capture and examine the value of a keystroke before it is displayed on the screen. I have made good use of this for single character fields where I want to examine if the value is correct and also convert the value to upper case like so:

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1.  
2. <input 
3.    type="text" 
4.    name="f1" 
5.    id  ="f1"  
6.    maxLength="1"
7.    onKeyPress="return isHorS(event);" 
8.  />
9.  
10. function isHorS(evt)
11. {
12.    evt = (evt) ? evt : event; 
13.    var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode : ((evt.which) ? evt.which : 0));   
14.  
15.       if (charCode != 8 && charCode != 9 && charCode != 32 && charCode != 72 && charCode != 104 && charCode != 83 && charCode != 115 )
16.       {  
17.             alert("You must either leave blank or enter H or S!"); 
18.              document.getElementById("f1").value = "";
19.       }else{
20.           if (charCode == 104  || charCode == 115 )
21.           {
22.             var cUp = String.fromCharCode(charCode)
23.             document.getElementById("f1").value = cUp.toUpperCase();
24.           }
25.       }
26.  
27. }
28.  

As I said this works great when I am only dealing with one character. But for longer strings than one character, I would like to prevent unwanted characters from becoming part of the string. Can I use this technique by intercepting what the user is typing give them an alert and then cancel that keystroke entry?

[Logician]

It's much simpler to use a regular expression to remove unwanted characters from the string after each keystroke. Use the onkeyup event.

[Claus Mygind]

great do you have an example I can use. although I did get it to work like this:

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1.  onKeyPress=" return isValidCode(event, this);"
2.  
3. function isValidCode(evt, obj)
4. {
5.    evt = (evt) ? evt : event; 
6.    var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode :  
7.        ((evt.which) ? evt.which : 0));   
8.     if ( charCode == 8 || 
9.          charCode == 9 || 
10.         (charCode > 47 && charCode < 58) || 
11.         (charCode > 64 && charCode < 91) ||    
12.         (charCode > 96 && charCode < 123) )
13.     {
14.         if (charCode > 96 && charCode < 123)
15.         {
16.             Here I would like to make it an uppercase value
17.         }
18.     }else{
19.         alert("That is not a valid character ");
20.         return false;
21.     }
22. }
23.  
24.  

Perhaps your example of a regular expression can also convert the keystroke upper case if allowed?

[Claus Mygind]

Ok I have learned that only IE let's you intercept a keystroke and alter it before it reaches the form (generally considered a security risk as programmer can alter what the user is entering)

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1. var charCode = event.keyCode;
2.  
3. event.keyCode = charCode - 32

And as I am working exclusively with fireFox that will not work for me.

will look at the keyup option