onsubmit.js

这是《JavaScript学习源代码》一书的源代码

// a function to validate an email address
function send_if_valid()
{ 
  // look for an @ character
  if( document.forms.f.email.value.indexOf("@")== -1 || document.forms.f.email.value.indexOf(".")== -1 )
  {
    
   // if absent display a message
    
  alert( "Email address is absent or incorrect" );
    
  // ...and do not submit the form
    
  return false;
   
  }                    
}