Checking textbox for illegal characters w/ Javascript

I am working on a form, with several text boxes on it. I would like to know how I can go about trying to check for certain characters. Currently I am just checking if the text boxes have something in them. with the following code.

(isEmpty(document.guestform.visitorname.value.toString()))
{ alert("You need to provide a name.");
document.guestform.vistorname.focus(); return false; }

How can I incorportate into this or after this piece of code something that will check if a "\" or a "/" is found. I need to check for this because \ / is not part of a valid name.

I am using javascript.

Thanks to all that help out.

I really appreciate your help.

Use a regular expression search to get what you want. Try this example (let me know if you need an explanation of what is happening in "searchpattern"):

Code:

---

<script language="JavaScript">
var searchpattern = /(\\|\/)+/

function CheckString(FString){
if(FString.search(searchpattern) != -1){
alert("You can not enter a \\ or a / into the field.")
}
}
</script>

<form name="MyForm">
<input type="text" name="MyText" value="Hell/0 World!" onblur="CheckString(this.value)">
<input type="submit">
</form>

---

RealisticGraphics, thanks for the code. No need to explain, I see what is going on in it.

Thanks for your help.

No problem!