. Net client data verification instance

Aretrial Code Block < Form ID = "Form1" Runat = "Server" >
< ASP: textbox ID = "Textbox1" Runat = "Server" > </ ASP: textbox >
< ASP: button ID = "Button7" Runat = "Server" Onclick = "Button7_click" Onclientclick = "Javascript: Return checkform ()" Text = "Submit"   />
</ Form >

JavaScript code block < Script Language = " Javascript " Type = " Text/JavaScript " >

Function checkform () {
If (Document. form1.textbox1. Value =   "" ) {
Alert ("Why is it empty!");
Document. form1.textbox1. Focus ();
Return False;
}
VaR Length = Document. form1.textbox1. value. length;
If (Length <   6   | Length >   10 ) {
Alert ("It must be 6 ~ Within 10 characters!");
Return False;
}
}

</ Script >