Form form submission no page refresh (non-JS)

Read a piece of code first (php example)

1. Form code (form.php):

<?phpheader ("content-type:text/html; Charset=utf8 ");? ><iframe name= "Testiframename" style= "Display:none;" ></iframe><form target= "Testiframename" method= "post" action= "formaction.php" ><input type= "text" Name= "username"/><input type= "password" name= "password"/><input type= "Submit" value= "Submit"/></form >

2. Action code (formaction.php):

<?phpecho "<script>alert (' Test .... ');</script>";? >

OK, the above code is very simple, but the implementation of the form submission no refresh .... What is this for?

Oh ~ actually very basic things ... Is the attribute problem of the form tag .....

Form form submission no page refresh (non-JS)