Function for validating a number

I have made a function for validating a text field. It is required that it is numeric. I have tried the code below, but the alert is activated when a "-" is entered. Can I use a IsNumeric method like in VB?

Code:

---

...
var err3 = 0;
var allowedchars = /\D/;
if ((allowedchars.test(document.cond.luftf.value)) || (allowedchars.test(parent.frames[1].navform.flow.value))) {
alert("ERROR");
err3 = 1;
...

---

}

Code:

---

<SCRIPT LANGUAGE="JAVASCRIPT"><!--
Function check(contents) {
    If (((contents / contents) != 1) && (contents != 0)) {alert('Please enter only a number into this text box')}
}
//--></SCRIPT>

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You can modify you matching string. If you want to allow numbers and -'s. Using parseInt() will give unpredictable results if you want to allow -'s. So will trying to divide the string into itself.

Let's say you wanted to match a US telephone number:

Code:

---

var allowed = /\(?\d{0,3}\)?-?\d{3}-\d{4}/;

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You might have to escape the -'s, I'm not sure.