Question

I want a regular expression for a textbox which allows only 3 digits and passes following criterias:

1. Only digits (234 or 123) or
2. Only one decimal at the end (55.1)
3. Should not allow spaces
4. If decimal is used then there should be a number after/before decimal as well (555. or 12. or .12 should not be allowed)

I have following RE which works partially:

/^\d{0,3}$|^\d{0,2}[\.]\d{1}$/

Any help in modifying this ?

Looks like problem is additional:

I am using the code at keypress. So it validates each pressed value at key press.

  if (window.event)    {
        knum = e.keyCode;
    }
    else if (e.which)    {
        knum = e.which;
    }
    kchar = String.fromCharCode(knum);
    numcheck = /^\d{0,3}$|^\d{0,2}[\.]\d{1}$/;

    alert(numcheck.test(kchar));

It returns false for any decimal key press. Even if I enter 55 and then try a decimal in middle to make it 5.5, ite returns false.

Answer 1

You need at least 1 digit, but 3 at most: \d{1,3}

OR

There have to be at least 1 but no more than 2 digits before and 1 after the decimal: \d{1,2}[.]\d

So these combined: /(^\d{1,3}$|^\d{1,2}[.]\d$)/

UPDATE:

You are testing the character which was added on the keypress event, not the full value of the input field. This would never have the expected result.

document.getElementById("yourfield").onkeyup = function(e) {

    // the event
    if (!e) e = window.event;

    // determine the target of the keyup event (the input field)
    var targ;
    if (e.target)
       targ = e.target;
    else if (e.srcElement)
       targ = e.srcElement;
    if (targ.nodeType == 3) // defeat Safari bug
       targ = targ.parentNode;

    // get the value
    kchar = targ.value;
    numcheck = /^\d{0,3}$|^\d{0,2}[\.]\d{1}$/;

    // test
    alert(numcheck.test(kchar));
}