Only allow numbers in an input field

jQuery_number_only.js

$.fn.numOnly = function() {
    return this.each( function() {
        // backspace(8), dot(.), tab(0) 0-9
        var c = [8, 0, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58];
        if ($(this).attr('type') === 'text') {
            $(this).keypress( function(e) {
                if (c.indexOf(e.which, c) == -1) {
                    e.preventDefault();
                }
            });
        }
    });
};

Whaddaya know, a ~4% speed increase! :P