Question

How to allow only one “.” in javascript during Keypress?

I have a code here:

function allowOneDot(txt) {

        if ((txt.value.split(".").length) > 1) {

          //here, It will return false; if the user type another "."

         } 
}

Answer 1

I will reiterate what I said in my comment before the answer:

And what if the user pastes in a bunch of periods? What if they edit the javascript in their console to completely ignore this check? Make sure you are handling validation correctly and not making too many simplifications.

Now that we’re proceeding at our own risk, here’s how you would not allow a user typing more than one . (period) in a textbox:

document.getElementById('yourTextboxIDHere').onkeypress = function (e) {
    // 46 is the keypress keyCode for period     
    // http://www.asquare.net/javascript/tests/KeyCode.html
    if (e.keyCode === 46 && this.value.split('.').length === 2) {
        return false;
    }
}

Working demo