Count Characters in TextArea (MultiLine TextBox) with Enter key (New Line) as 3 character using JavaScript

<label id="charsRemain">20</label>

<asp:HiddenField ID="hfMaxCharacter" runat="server" Value="20" />

<asp:TextBox ID="txtSmsMsg" runat="server" Rows="5" Columns="50" TextMode="MultiLine" onkeyup="myFunctionChars()"></asp:TextBox>

function myFunctionChars() {
 
    var txt = document.getElementById('<%=txtSmsMsg.ClientID %>').value;
    var max = document.getElementById('<%=hfMaxCharacter.ClientID %>').value;
    var leng = txt.length;
 
    var eachLine = txt.split('\n');
 
    leng += (eachLine.length - 1)
 
    if (leng <= max) {
 
        //var totalChars = $("#<%= this.hfMaxCharacter.ClientID %>").val() - leng;
            document.getElementById('charsRemain').innerHTML = max - leng;
        }
        else {
 
            var i = 0;
            var newTxt = txt.substr(0, max);
            var newLen;
            var originalLen;
            //alert(newTxt);
            //alert(newLen);
 
            while (i == 0) {
                originalLen = newTxt.length;
                newLen = newTxt.length;
                //alert(newLen + " - 1")
                var eachLine2 = newTxt.split('\n');
                newLen += (eachLine2.length - 1);
                //alert(newLen + " - 2")
                if (newLen <= max) {
                    //alert("i = 1");
                    i = 1;
                }
                else {
                    //alert(newLen + " - 3");
                    newTxt = newTxt.substr(0, originalLen - 1);
                    //alert(newTxt.length + " - 4");
                    i = 0;
                }
 
                document.getElementById('charsRemain').innerHTML = max - newLen;
                //alert(max + ' - ' + newLen)
                document.getElementById('<%=txtSmsMsg.ClientID %>').value = newTxt;
            }
 
        }
    }