Question

I’ve got four inputs that each take one number. What I want to do is set the focus automatically to the next input once the number has been set. They all have the class “inputs”.

This didn’t quite work:

$(".inputs").keydown(function () {

            $(this).next().focus();
        });

Answer 1

I would suggest setting maxlength as 1 to each textbox and switch to next one once the val.length and the maxlength is same.

DEMO

$(".inputs").keyup(function () {
    if (this.value.length == this.maxLength) {
      $(this).next('.inputs').focus();
    }
});

Edit: Spent some time for the following (not fully tested, but basic tests worked fine)

   1. Allowing just numeric chars  
   2. Allow some control like del, backspace, e.t.c
   3. Backspace on empty textbox will move to prev textbox
   4. charLimit var to dynamically decide how many char you want to restrict.

Code:

$(function() {
    var charLimit = 1;
    $(".inputs").keydown(function(e) {

        var keys = [8, 9, /*16, 17, 18,*/ 19, 20, 27, 33, 34, 35, 36, 37, 38, 39, 40, 45, 46, 144, 145];

        if (e.which == 8 && this.value.length == 0) {
            $(this).prev('.inputs').focus();
        } else if ($.inArray(e.which, keys) >= 0) {
            return true;
        } else if (this.value.length >= charLimit) {
            $(this).next('.inputs').focus();
            return false;
        } else if (e.shiftKey || e.which <= 48 || e.which >= 58) {
            return false;
        }
    }).keyup (function () {
        if (this.value.length >= charLimit) {
            $(this).next('.inputs').focus();
            return false;
        }
    });
});

DEMO