Javascript Email 格式判断 regular expression

function checkEmail(f,name){
 37     var emailPattern = /[A-Za-z0-9]+@[A-Za-z0-9]+\.[A-Za-z]{2,4}/;
 38     if(emailPattern.test(f[name].value)){
 39         return true;
 40     }
 41     alert("Email address incorrect!");
 42     f[name].focus();
 43     return false;
 44 }