Enable/Disable an asp:TextBox Control based on CheckBox.Checked true or false

[pFlyerb8]

I need to enable/disable an asp.TextBox/Input depending on a CheckBox. If the CheckBox.Checked = true then I need to enable the asp.TextBox/Input or if the CheckBox.Checked = false I then need need to disable the asp.TextBox/Input. Below is the code I have but it only works on first click, meaning if I check the box it will enable the asp.TextBox/Input but if I uncheck it will not disable the asp.TextBox/Input. Also, by default the asp.TextBox/Input is disable on Page_Load. \[code\]//If checked it should enable the input.//If unchecked it should disable the input.If Port is Required?<label class="checkbox"> <input type="checkbox" id="isportreqinput" name="isportreqinput" runat="server" onclick="fncport(this.form.isportreqinput, this.form.porttxt);" /> <span class="metro-checkbox">Check Me</span> </label>//This is the input I need to disable/enable depending on the checkbox<input type="text" name="porttxt" id="porttxt" runat="server" disabled="disabled" /> <script type="text/javascript"> function fncport(control, objname) { if (control.checked == true) { objname.disabled = false; } if (control.cheched == false) { objname.disabled = true } } </script>\[/code\]