Restrict to 2 decimal places in keypress of a text box?

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I want to enter a decimal point in a text box. I want to restrict the user by entering more than 2 digits after the decimal point. I have written the code for achieving that in the Keypress event.

function validateFloatKeyPress(el, evt) {
    var charCode = (evt.which) ? evt.which : event.keyCode;

    if (charCode != 46 && charCode > 31 && (charCode < 48 || charCode > 57)) {
        return false;
    }

    if (charCode == 46 && el.value.indexOf(".") !== -1) {
        return false;
    }

    if (el.value.indexOf(".") !== -1)
    {
        var range = document.selection.createRange();

        if (range.text != ""){
        }
        else
        {
            var number = el.value.split('.');
            if (number.length == 2 && number[1].length > 1)
                return false;
        }
    }

    return true;
}
<asp:TextBox ID="txtTeamSizeCount" runat="server" onkeypress="return validateFloatKeyPress(this,event);" Width="100px" MaxLength="6"></asp:TextBox>

The code is working but the issue is: if I enter “.75” and then change it to “1.75”, it is not possible. Only way to do it is delete it completely and then type “1.75”. This issue occurs if there are already 2 digits after decimal in the textbox. The conditions that I impose are

a) After decimal is present, it must at least have 1 or 2 digits. For ex .75 or .7 or 10.75 or 333.55 or 333.2 is accepted. but not .753 or 12.3335


b) Before the decimal, it not a must for the user to enter a value. User must also be able to enter integer numbers also.

Can you tell me what could be the issue?

Thanks,
Jollyguy

Answer

You were almost there. Just check that there are no more than 2 characters after the decimal.

UPDATE 1 – check carat position to allow character insertion before the decimal.
UPDATE 2 – correct issue pointed out by ddlab’s comment and only allow one dot.

 function validateFloatKeyPress(el, evt) {
    var charCode = (evt.which) ? evt.which : event.keyCode;
    var number = el.value.split('.');
    if (charCode != 46 && charCode > 31 && (charCode < 48 || charCode > 57)) {
        return false;
    }
    //just one dot (thanks ddlab)
    if(number.length>1 && charCode == 46){
         return false;
    }
    //get the carat position
    var caratPos = getSelectionStart(el);
    var dotPos = el.value.indexOf(".");
    if( caratPos > dotPos && dotPos>-1 && (number[1].length > 1)){
        return false;
    }
    return true;
}

//thanks: http://javascript.nwbox.com/cursor_position/
function getSelectionStart(o) {
    if (o.createTextRange) {
        var r = document.selection.createRange().duplicate()
        r.moveEnd('character', o.value.length)
        if (r.text == '') return o.value.length
        return o.value.lastIndexOf(r.text)
    } else return o.selectionStart
}

http://jsfiddle.net/S9G8C/1/
http://jsfiddle.net/S9G8C/203/



Source: stackoverflow