JavaScript无法验证字段

Question

我有以下代码片段。 由于某种原因，验证无效。

我想验证两件事：

1. 没有文本字段留空
2. 密码字段至少有8个字符

如果其中任何一个是假的，我应该得到一个错误。 但是这个错误消息永远不会显示出来。 以下是片段：

 function validate() { if (document.getElementById("name").value == '') { document.getElementById("errorMsg").value=="You have forgotten to enter your name"; } else if (document.getElementById("surname").value == '') { document.getElementById("errorMsg").value == "You have forgotten to enter your surname"; } else if (document.getElementById("email").value == '') { document.getElementById("errorMsg").value == "You have forgotten to enter your email address"; } } 

 * { margin: 0px; padding: 0px; } #title{ font: bold 20px Tahoma; color: white; margin: 10px; text-align: left; width: 80%; } #header{ padding: 80px; font: 14px Tahoma; } body{ width:100%; display:-webkit-box; -webkit-box-pack: center; } #main_container{ max-width: 1000px; margin: 10px 0px; display: -webkit-box; -webkit-box-orient: vertical; -webkit-box-flex: 1; } #control-container{ display:-webkit-box; -webkit-box-orient: horizontal; } #label-container{ -webkit-box-flex: 1; margin: 10px; } p { font: 14px Tahoma; margin: 20px; width: 350px; height: 30px; } #element-container{ width: 500px; margin: 20px 0px; display: -webkit-box; -webkit-box-orient: vertical; } #name{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #surname{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #email{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #password{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } input[type="text"]:focus{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="text"]:hover{ border: 1px solid #999; } input[type="text"]:focus:hover{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="password"]:focus{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="password"]:hover{ border: 1px solid #999; border-radius: 0px; } input[type="password"]:focus:hover{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; border-radius:0; } #register{ font: 14px Tahoma; margin: 20px; text-align: center; } #btnRegister { width: 100px; height: 30px; margin: 20px; text-align: center; } 

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Fastloader - Register for a new account</title> <link rel="stylesheet" href="register.css"> <script src="register.js"></script> </head> <body> <div id = "main-container"> <header id = "header"> <h1>Register for a new account<h1> </header> <div id= "control-container"> <section id ="label-container"> <p><label>Enter your Name:</label></p> <p><label>Enter your Surname:</label></p> <p><label>Enter your Email address:</label></p> <p><label>Choose a strong Password:</label></p> </section> <section id = "element-container"> <div id = "name"> <input name="Name" type="text" id="name"/> </div> <div id = "surname"> <input name="Surname" type="text" id="surname"/> </div> <div id = "email"> <input name="Email" type="text" id="email" /> </div> <div id = "password"> <input name="Password" type="password" id = "password"/> </div> </section> </div> <footer id = "register"> <div id = "agreement"> <label>I have read the Terms and Conditions:</label> <input name="agree" type="checkbox" id="agree" /> </div> <div id = "error"> <p><label id = "errorMsg"></label></p> </div> <div id = "button"> <input type = "button" id="btnRegister" value = "Register" onclick="validate();"/> </div> </footer> </div> </body> </html> 

Answer 1

document.getElementById("errorMsg").value == "You have forgotten to enter your email address";

1. 您使用==进行比较，而不是设置新值。 你必须只使用=

2. Label没有value ，正确的方法是.innerText

Answer 2

这就是我设法解决它的方法：

 function validate() { if (document.getElementById('name').value.length == 0) { alert("You have forgotten to enter your name"); } else if (document.getElementById("surname").value.length == 0) { alert("You have forgotten to enter your surname"); } else if (document.getElementById("email").value.length == 0) { alert("You have forgotten to enter your email address"); } } 

 * { margin: 0px; padding: 0px; } #title{ font: bold 20px Tahoma; color: white; margin: 10px; text-align: left; width: 80%; } #header{ padding: 80px; font: 14px Tahoma; } body{ width:100%; display:-webkit-box; -webkit-box-pack: center; } #main_container{ max-width: 1000px; margin: 10px 0px; display: -webkit-box; -webkit-box-orient: vertical; -webkit-box-flex: 1; } #control-container{ display:-webkit-box; -webkit-box-orient: horizontal; } #label-container{ -webkit-box-flex: 1; margin: 10px; } p { font: 14px Tahoma; margin: 20px; width: 350px; height: 30px; } #element-container{ width: 500px; margin: 20px 0px; display: -webkit-box; -webkit-box-orient: vertical; } #name{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #surname{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #email{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } #password{ font: 14px Tahoma; margin: 10px; width: 350px; height: 30px; } input[type="text"]:focus{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="text"]:hover{ border: 1px solid #999; } input[type="text"]:focus:hover{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="password"]:focus{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; } input[type="password"]:hover{ border: 1px solid #999; border-radius: 0px; } input[type="password"]:focus:hover{ outline: none; box-shadow: 0px 0px 5px #7f0000; border:1px solid #b20000; border-radius:0; } #register{ font: 14px Tahoma; margin: 20px; text-align: center; } #btnRegister { width: 100px; height: 30px; margin: 20px; text-align: center; } 

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Fastloader - Register for a new account</title> <link rel="stylesheet" href="register.css"> <script src="register.js"></script> </head> <body> <div id = "main-container"> <header id = "header"> <h1>Register for a new account<h1> </header> <div id= "control-container"> <section id ="label-container"> <p><label>Enter your Name:</label></p> <p><label>Enter your Surname:</label></p> <p><label>Enter your Email address:</label></p> <p><label>Choose a strong Password:</label></p> </section> <section id = "element-container"> <div id = "name_container"> <input name="Name" type="text" id="name"/> </div> <div id = "surname_container"> <input name="Surname" type="text" id="surname"/> </div> <div id = "email_container"> <input name="Email" type="text" id="email" /> </div> <div id = "password_container"> <input name="Password" type="password" id = "password"/> </div> </section> </div> <footer id = "register"> <div id = "agreement"> <label>I have read the Terms and Conditions:</label> <input name="agree" type="checkbox" id="agree" /> </div> <div id = "error"> <p><label id = "errorMsg"></label></p> </div> <div id = "button"> <input type = "button" id="btnRegister" value = "Register" onclick="validate();"/> </div> </footer> </div> </body> </html>