一般有两种方法：一是通过innerHTML来添加元素；二是通过appendChild()来添加。
区别是：前者添加后，不会立即生效；而后者则会立即生效。
例子：
静态页面：
<html> <head> <script type="text/javascript">
function loginSubmit(name_input_control_name, password_input_control_name, username, userpwd, destUrl){
var userName = document.getElementById("auto_login_username"); var password = document.getElementById("auto_login_password"); var login = document.getElementById("form_auto_login_by_fengyf"); userName.name = name_input_control_name; password.name = password_input_control_name; userName.value = username; password.value = userpwd; login.action = destUrl; login.submit();
} </script> </head> <body> <div id="div_auto_login"> <form id="form_auto_login_by_fengyf" action="" method="post" target="_self"> <input type="text" id="auto_login_username" /> <input type="password" id="auto_login_password" /> <form> </div> <input type="button" value="登录百度空间" onclick="javascript: loginSubmit('username', 'password', 'shcswlkj', 'chengshan', 'https://passport.baidu.com/?login')"> </body></html>采用js动态添加——通过innerHTML：
<html> <head> <script type="text/javascript"> function loginSubmit(name_input_control_name, password_input_control_name, username, userpwd, destUrl){ var div_login = document.createElement("div"); div_login.style.cssText = "display:block;"; document.body.appendChild(div_login); div_login.innerHTML = "<form id='auto_login_form_by_fengyf' method='post' action='' target='_self'>"; div_login.innerHTML += "<input type='text' id='auto_login_username'>"; div_login.innerHTML += "<input type='password' id='auto_login_password'>"; div_login.innerHTML += "</form>"; var userName = document.getElementById("auto_login_username"); var password = document.getElementById("auto_login_password"); var login = document.getElementById("auto_login_form_by_fengyf"); userName.name = name_input_control_name; password.name = password_input_control_name; userName.value = username; password.value = userpwd; login.action = destUrl; //login.submit(); } </script> </head> <body> <input type="button" value="登录百度空间" onclick="javascript: loginSubmit('username', 'password', 'shcswlkj', 'chengshan', 'https://passport.baidu.com/?login')"> </body></html>动态创建网页元素——通过createElement()和appendChild()：
<html> <head> <script type="text/javascript"> function loginSubmit(name_input_control_name, password_input_control_name, username, userpwd, destUrl){ var div_login = document.createElement("div"); div_login.style.cssText = "border:0px;"; div_login.style.display = "block"; document.body.appendChild(div_login); var form_auto_login = document.createElement("form"); form_auto_login.id = "auto_login_form_by_fengyf"; form_auto_login.method = "post"; form_auto_login.action = destUrl; div_login.appendChild(form_auto_login); var text_username = document.createElement("input"); text_username.type = "text"; text_username.id = "auto_login_username"; text_username.name = name_input_control_name; text_username.value = username; form_auto_login.appendChild(text_username); var text_userpwd = document.createElement("input"); text_userpwd.type = "password"; text_userpwd.id = "auto_login_password"; text_userpwd.name = password_input_control_name; text_userpwd.value = userpwd; form_auto_login.appendChild(text_userpwd); form_auto_login.submit(); } </script> </head> <body> <input type="button" value="登录百度空间" onclick="javascript: loginSubmit('username', 'password', 'shcswlkj', 'chengshan', 'https://passport.baidu.com/?login')"> <input type="button" value="登录126邮箱" onclick="javascript: loginSubmit('user', 'password', 'chaomengyuexiang', 'a11314a11314', 'http://entry.126.com/cgi/login')"> <a href="http://entry.126.com/cgi/login?domain=126.com&language=0&bCookie&user=chaomengyuexiang&pass=a11314a11314">登录126邮箱</a> </body></html>这3种情况下，第二种情况，即通过innerHTML的方式来动态创建网页元素时，被动态创建的表单form无法提交，而第三种情况，即通过createElement()和
appendChild()的方式动态创建的表单form便可以提交：submit()。