I have a text field, whose value I am reading. I want to only allow alphanumeric characters and hyphen - value.

The regex I have so far doesn't seem to fire if I enter values like abc$d or w2w,2 or we&*23 etc.

var someName = document.getElementById("sometextField");
if(/^[a-z0-9-]+$/i.test(someName.value))
{
    alert('Name can only be alpha numeric with hypen.');
    return;
}

Please help. Thanks for your help and time.

I have a text field, whose value I am reading. I want to only allow alphanumeric characters and hyphen - value.

The regex I have so far doesn't seem to fire if I enter values like abc$d or w2w,2 or we&*23 etc.

var someName = document.getElementById("sometextField");
if(/^[a-z0-9-]+$/i.test(someName.value))
{
    alert('Name can only be alpha numeric with hypen.');
    return;
}

Please help. Thanks for your help and time.

• javascript
• regex

• from where is this being called? (or is it?) Is this in onChange or onBlur or in a form onSubmit handler…? – BRPocock Commented Dec 28, 2011 at 21:16
• @BRPocock that shouldn't matter where's called from. The code snippet should fire if the condition is not met. – Nomad Commented Dec 28, 2011 at 21:22
• Curious if it were actually being called, since it seems to be correct, as written, my assumption was the handler wasn't connected or sommat. – BRPocock Commented Dec 28, 2011 at 21:31

2 Answers 2

Access the input's value property:

if(!/^[a-z0-9-]+$/i.test(someName.value)) {
   //-------------------------^^^^^^^^^^
   alert('Name can only be alpha numeric with hypen.');
   return;
}

Update

To allow a hyphen only in the middle of the expression, not at the beginning or end, you can use the following. There are likely to be better ways, but this should do the job. You have three groups of [a-z0-9]+, but the middle one also permits -. The start and end groups don't permit -.

/^[a-z0-9]+[a-z0-9-]+[a-z0-9]+$/

Notice that "-" is a special character. I don't know whether the regex engine of the browsers consider it been a special character. But I would reend you to escape it as "[a-z0-9\-]". Also, the negation should be put inside the class, as "[^a-z0-9\-]". And finally, it shouldn't contain a start and end mark (^ and $). So, I think it would be like /[^a-z0-9\-]/.test(...)