How to count character of TextBox in ASP.NET

Introduction

Here, we will see how to check the number of character has been inserted in the TextBox. A TextBox Which has max length 120 character and we insert a character in TextBox max length will be display 119 characters. When We enter 120 characters in the TextBox that will be the Max length.

Drag and drop a TextBox on the page. Select TextBox and press F4 to the property window.

TextMode="MultiLine"

Now add the following code in the Head section of the .aspx page.

<head runat="server">
<title></title>
<style type="text/css">
.valid
{
background-color: #FFFFFF;
color: #000000;
}
.invalid
{
background-color: #FFCCCC;
color: #ff0000;
}
</style>
<script language="javascript">
function textCounter1(field, maxlimit)
{
if (field.value.length > maxlimit)
{
field.value = field.value.substring(0, maxlimit);
document.getElementById('message').className = "invalid";
document.getElementById('message').focus(); //alert('You have reached your maximum character limit.');}
else
{
document.getElementById('message').className = "valid";
}
}
function textCounter(field, countfield, maxlimit)
{
if (field.value.length > maxlimit) // if too long...trim it!
field.value = field.value.substring(0, maxlimit);
else
countfield.value = maxlimit - field.value.length;
}
</script>
</head>

Now add the following code in the body section.

<body bgcolor="#FFFFFF">
<form name="blah" action="" method="post" runat="server">
<asp:TextBox ID="message" runat="server" name="message" onkeydown="textCounter(this.form.message,this.form.remLen,120)" onkeyup="textCounter1(this.form.message, 120)" class="validentry" Height="101px" TextMode="MultiLine" Width="228px"></asp:TextBox>
<br/>
<input readonly type="text" name="remLen" size="3" maxlength="3" value="120" position: absolute; style="width: 34px">Character left
<br/>
<br/>
<br/>
</form>
</body>

Now run the application and check number of character has been inserted in the TextBox.

Figure1

Now Insert max length characters in TextBox.

Figure2