[英]Javascript skipping the if and if else conditions and directly jumping to else condition
我是JavaScript新手，只是嘗試通過簡單的登錄頁面使用JavaScript。
我已經使用HTML，CSS和JavaScript創建了一個登錄頁面以進行驗證。 但是我的JavaScript代碼無法正常工作。
它跳過if條件，直接跳到else部分，有時只是驗證第一個if else部分以進行用戶名驗證。
以下是我的JavaScript和html代碼。 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，從該方法本身的名稱（獲取Elements ByName）中，您知道該方法返回名稱為用戶名的節點列表集合。 因此您需要提供正確的索引號才能獲取該值。 否則，您還可以通過在HTML中為文本字段定義ID來使用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，您想為用戶名和密碼添加一些驗證。 您在第一條if語句中編寫的內容是為了驗證兩者是否均有效並且應該正常工作。
else if(username == null || username == ""){
alert("Please enter CEC ID");
}
如果用戶名無效，這將停止進一步評估。 萬一您想檢查密碼是否也是無效的，您將需要寫一個不同的if / else塊，而不要繼續進行用戶名驗證。
您正在使用document.getElementsByName ，根據您的代碼，您將在username和password得到undefined 。 因此，您需要這樣做：
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：
如果要防止在提交時不清除字段，則可以使用事件對象的preventDefault方法，如下所示：
$("#Formid").submit(function(event){
event.preventDefault()
})
要么
$("#Formid").submit(function(event){
e.returnValue = false;
})
嘗試這個 ：
var username = document.getElementsByName("username")[0].value;
var password = document.getElementsByName("password")[0].value;
或在您的元素上設置ID並嘗試：
var username = document.getElementById("username").value;
var password = document.getElementById("password").value;
您應分開驗證用戶輸入和檢查用戶憑據，以使代碼清晰易讀，請參考以下代碼：
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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