Question

I have a textbox where I want only allowed up to 11 digits, an optional comma, and two more digits after it. Anything else should not be rendered when the key is pressed into the textbox:

$('#txt').keypress(function (e) {
  var code = e.which;
  var key = String.fromCharCode(code);
  // REGEX TO AVOID CHARS & A DOT (.)
  var pattern = /[a-zA-Z]|\./g;
  var isMatch = pattern.test(key);
  if (isMatch) {
    // DO NOT RENDER CHARS & dot
    e.preventDefault();
  }
});

The above code works when an invalid key is pressed, such as a char or a dot, but does not ensure only one comma and only 2 digits afterwards.

This must match:

12314
123123,44

This must not:

12313,6666

Here is a demo.

UPDATE:
Any digit except numbers and comma must be avoided, so the regex I proposed is not valid since only prevents dots (.).

Answer 1

You should test your complete string, not only the current letter.

$('#txt').keypress(function (e) {
    var key = String.fromCharCode(e.which);
    var pattern=/^[0-9]{1,11}(,[0-9]{0,2})?$/;

    // test this
    var txt = $(this).val() + key;

    if (!pattern.test(txt)) {
        e.preventDefault();
    }
});

​

jsfiddle example