Why can't a onsubmit submit false-CodePudding

 & lt; ! DOCTYPE html> 
 
<meta charset="utf-8" & gt; 
<meta HTTP - equiv="X - UA - Compatible" content="IE=edge" & gt; 
<meta name="viewport" content="width=device - width, initial - scale=1.0" & gt; 
 Document The function checkUser () {
Var uname=document. QuerySelector (" # "UN"). The value; 
Var len=uname. Length; 
Var ino=uname. ToLowercase. IndexOf (" admin "); 
If (len<3 | | len> 30 | | ino!=1) {
Alert (" username illegal!" ); 
return false; 
} 
return true; 
} 
</script> 
 
<body> 
 
User name: & lt; Input type="text" id="UN" & gt;