Run a javascript function when my focus changes.

I just found out how to do it.

If someone else have the same problem, you can simply add a new Attribute to your text box. so in your server side just use the code below:

TextBox.Attributes.Add("onblur", "return Function();");

I hope that will help.

Try to add

TextBox.Attributes.Add("onblur", "return Function();");

in Page_Load event it will solve your problem