[英]Javascript skipping the if and if else conditions and directly jumping to else condition
我是JavaScript新手，只是尝试通过简单的登录页面使用JavaScript。
我已经使用HTML，CSS和JavaScript创建了一个登录页面以进行验证。 但是我的JavaScript代码无法正常工作。
它跳过if条件，直接跳到else部分，有时只是验证第一个if else部分以进行用户名验证。
以下是我的JavaScript和html代码。 我正在使用外部JavaScript。
function ValidateSignIn() { //Variable declarations and initialization var username = document.getElementsByName("username").value; var password = document.getElementsByName("password").value; //Validation of username and password fields if (username == "Temp" && password == "123") { alert("Login Successful!!"); window.location = "C:\\Users\\metyagi\\Downloads\\Personal data\\THE SCM QUIZ\\WelcomePage.html"; } else if (username == null || username == "") { alert("Please enter CEC ID"); } else if (password == null || password == "") { alert("Please enter Password"); } else { alert("Username or Password is incorrect, Please try again!!"); } }
<!doctype html> <html> <head> <meta charset="utf-8"> <title>The SCM Quiz Login Page</title> <link rel="stylesheet" type="text/css" href="css\\SignIn.css" /> <script type="text/javascript" src="C:\\Users\\mt\\Downloads\\data\\test\\SignIn.js"></script> </head> <body> <!--Div for Logo--> <Div class="logo"> <img src="images\\logo.png" /> </Div> <!--Div for form--> <Div class="loginform"> <h3>Login </h3> <h6>Required fields are marked with *</h6> <form method="post" action="" name="SignIn"> <INPUT TYPE="text" name="username" placeholder="Please Enter Username*"> </br> </br> <INPUT TYPE="password" name="password" placeholder="Please Enter Password*"> </br> </br> <INPUT TYPE="submit" name="SignIn" value="SIGN IN" onclick="ValidateSignIn()"> <a href="ForgotPassword.html">Forgot Password?</a> <p class="message">Not Registered Yet? <a href="SignUp.html">Sign Up!</a> </P> </form> </Div> </body> </html>
您正在使用document.getElementsByName（“ username”）方法，从该方法本身的名称（获取Elements ByName）中，您知道该方法返回名称为用户名的节点列表集合。 因此您需要提供正确的索引号才能获取该值。 否则，您还可以通过在HTML中为文本字段定义ID来使用getElementById（）方法。
function ValidateSignIn() { //Variable declarations and initialization var username = document.getElementsByName("username")[0].value; var password = document.getElementsByName("password")[0].value; //Validation of username and password fields if (username == "Temp" && password == "123") { alert("Login Successful!!"); window.location = "C:\\Users\\metyagi\\Downloads\\Personal data\\THE SCM QUIZ\\WelcomePage.html"; } else if (username == null || username == "") { alert("Please enter CEC ID"); } else if (password == null || password == "") { alert("Please enter Password"); } else { alert("Username or Password is incorrect, Please try again!!"); } }
<html> <head> <meta charset="utf-8"> <title>The SCM Quiz Login Page</title> <link rel="stylesheet" type="text/css" href="css\\SignIn.css" /> <script type="text/javascript" src="C:\\Users\\mt\\Downloads\\data\\test\\SignIn.js"></script> </head> <body> <!--Div for Logo--> <Div class="logo"> <img src="images\\logo.png" /> </Div> <!--Div for form--> <Div class="loginform"> <h3>Login </h3> <h6>Required fields are marked with *</h6> <form method="post" action="" name="SignIn"> <INPUT TYPE="text" name="username" placeholder="Please Enter Username*"> </br> </br> <INPUT TYPE="password" name="password" placeholder="Please Enter Password*"> </br> </br> <INPUT TYPE="submit" name="SignIn" value="SIGN IN" onclick="ValidateSignIn()"> <a href="ForgotPassword.html">Forgot Password?</a> <p class="message">Not Registered Yet? <a href="SignUp.html">Sign Up!</a> </P> </form> </Div> </body> </html>
基本上，您想为用户名和密码添加一些验证。 您在第一条if语句中编写的内容是为了验证两者是否均有效并且应该正常工作。
else if(username == null || username == ""){
alert("Please enter CEC ID");
}
如果用户名无效，这将停止进一步评估。 万一您想检查密码是否也是无效的，您将需要写一个不同的if / else块，而不要继续进行用户名验证。
您正在使用document.getElementsByName ，根据您的代码，您将在username和password得到undefined 。 因此，您需要这样做：
function ValidateSignIn()
{
//Variable declarations and initialization
var username = document.getElementsByName("username")[0].value;
var password = document.getElementsByName("password")[0].value;
//Validation of username and password fields
if(username == "Temp" && password == "123")
{
alert("Login Successful!!");
window.location = "C:\Users\metyagi\Downloads\Personal data\THE SCM QUIZ\WelcomePage.html";
}
else if(username == null || username == "")
{
alert("Please enter CEC ID");
}
else if (password == null || password == "")
{
alert("Please enter Password");
}
else
{
alert("Username or Password is incorrect, Please try again!!");
}
}
UPDATE1：
如果要防止在提交时不清除字段，则可以使用事件对象的preventDefault方法，如下所示：
$("#Formid").submit(function(event){
event.preventDefault()
})
要么
$("#Formid").submit(function(event){
e.returnValue = false;
})
尝试这个 ：
var username = document.getElementsByName("username")[0].value;
var password = document.getElementsByName("password")[0].value;
或在您的元素上设置ID并尝试：
var username = document.getElementById("username").value;
var password = document.getElementById("password").value;
您应分开验证用户输入和检查用户凭据，以使代码清晰易读，请参考以下代码：
function ValidateSignIn(){
var hasError = false;
//Variable declarations and initialization
var username = document.getElementsByName("username")[0].value;
var password = document.getElementsByName("password")[0].value;
//Validation of username and password fields
if (!username) { // this will check null, undefined, and empty string
hasError = true;
alert("Please enter CEC ID");
} else if (!password) {
hasError = true;
alert("Please enter Password");
}
if (!hasError) {
if(username == "Temp" && password == "123"){
alert("Login Successful!!");
window.location = "C:\Users\metyagi\Downloads\Personal data\THE SCM QUIZ\WelcomePage.html";
} else {
alert("Username or Password is incorrect, Please try again!!");
}
}
}
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