asp.net onkeyup event for textbox

Question

I have an issue with onkeyup event with textbox. my function is to check password strength of the password textbox. so when a users enter his password, it will call the func

Answer 1

Every control that is included in an ASP.NET Web page must contain a unique identifier (ID). To maintain this uniqueness ASP.Net change the ID of control when the page gets rendered into HTML.

Here, if below control is inside <asp:ContentPlaceHolder> then the ID is likely to gets changed into ctl00$ctl00$ContentPlaceHolder$tb_password for example.

<asp:TextBox ID="tb_password" runat="server" TextMode="Password" onKeyUp="checkPasswordStrength()"></asp:TextBox>

To overcome this what you can do it either use Client Mode in mark-up or use ClientID in javascript.

Method 1:

<asp:TextBox ID="tb_password" runat="server" TextMode="Password" onKeyUp="checkPasswordStrength()" ClientMode="Static"></asp:TextBox>

Method 2:

var passwordTextbox = document.getElementById("<%=tb_password.ClientID%>");
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document.getElementById("<%=lbl_passwordStrength.ClientID%>").innerHTML = strength;
passwordTextbox.style.color = "white";
passwordTextbox.style.backgroundColor = backgroundColor;