Javascript regex only alphabet, number and underscore

Question

I want to check if a text box input is valid (only alphabet, numbers and underscores allowed. No whitespaces or dashes). I currently have this, but whitespaces & dashes seem to pass.

function validText(field)
{
    var re = /[a-zA-Z0-9\-\_]$/
    if (field.value.search(re) == -1)
    {
        alert ("Invalid Text");
        return false;
    }
}

A valid input would be something like

'Valid_Input123'

invalid

'Invalid-Input !'

Answer 1

1. The \w is a handy regex escape sequence that covers letters, numbers and the underscore character
2. You should test the entire string for valid characters by anchoring the validity test at the start (^) and end ($) of the expression
3. The regular expression test method is faster than the string search method
4. You can also test for one or more characters using the + quantifier

To summarise (in code)

var re = /^\w+$/;
if (!re.test(field.value)) {
    alert('Invalid Text');
    return false;
}
return true;

Alternatively, you can test for any invalid characters using

/\W/.test(field.value)

\W being any character other than letters, numbers or the underscore character.

Then you might also need to add a length check to invalidate empty strings, eg

if (/\W/.test(field.value) || field.value.length === 0)