How do I .addClass() when a regex condition is matched, using JQuery?

I have the following code, see below:

$(document).ready(function(){

   var prefixNumber = $('.numeric').val();

   if(prefixNumber.match(????){
      prefixNumber.addClass('.field-error');
   }    

});

What I'm looking to happen is when the user types something in the input.numeric field a开发者_如何学Gond it doesnt match one of these numbers, say...1, 3, 8 or 999 a class .field-error is added to the input field which has a red background colour. Kind of trying to make a live error notification if that makes sense.

Any help would be greatly appreciated, Thanks

Use a change handler on your input:

$('.numeric').change(function () {
    $(this).toggleClass('field-error', /[^0-9]/.test(this.value));
});

If you only have a couple of numbers, there is no need for regex (especially as they don't have a pattern). You can use an object instead:

var valid = {
   1: true,
   3: true,
   8: true,
   999: true
};

Then you have to decide when to evaluate the value. If it is while the user is typing, listen to the keyup (or keydown) event:

var timer = null;

function validate() {
     var val = $('.numeric').val()
     $('.numeric').toggleClass('field-error',  val !=='' && !valid[+val]);
}

$('.numeric').keyup(function() {
    clearTimeout(timer);
    setTimeout(validate, 400); // time has to be adjusted...
});

DEMO

Try:

if (!prefixNumber.match(/^\d+$/)) {...}

It forces the prefixNumber to only consist of digits.

$(document).ready(function(){

   var prefixNumber = $('.numeric');

   if(!prefixNumber.val().match(/^(1|3|8)$/){
      prefixNumber.addClass('field-error');
   }    

});

That would display an error if the input isn't 1, 3 or 8 :)

Moved your val() method.