Develop Reference

Simple Login Form

I am trying to implement a simple login form using JavaScript and HTML. When I submit the form, I want to check the username and password against a list of valid credentials.
If the credentials are valid, I want to redirect the user to the home page. Otherwise, I want to show an error message. I have written the following code, but it is not working as expected. Can someone please help me debug this issue?
<form id="login-form">
<label for="username">Username:</label><br>
<input type="text" id="username" name="username"><br>
<label for="password">Password:</label><br>
<input type="password" id="password" name="password"><br><br>
<input type="submit" value="Submit">
</form>
<script>
const form = document.getElementById('login-form');
const username = document.getElementById('username');
const password = document.getElementById('password');
form.addEventListener('submit', function(event) {
event.preventDefault();
const validCredentials = [
{ username: 'user1', password: 'pass1' },
{ username: 'user2', password: 'pass2' }
];
for (const credential of validCredentials) {
if (credential.username === username.value && credential.password === password.value) {
window.location.href = '/home';
} else {
alert('Invalid username or password');
}
}
});
</script>
I am implement a simple login form using JavaScript and HTML.
The expected outcome of the code is that when the user enters a valid username and password and clicks the submit button, they will be redirected to the home page. If the username and password are invalid, an error message should be displayed.

First of all, don't do this if you want to use this code for real users and production web app. It's not a good approach to hardcore users or passwords in a JavaScript script. If you are using this code for learning purposes, it's okay!
Secondly, the code has two meaningful problems. The alert inside the else block is running after every iteration of the for loop. You have to add a return statement to stop the loop and exists the function. Place the alert after the for loop, because the intention of the alert (I guess) is: if you don't find any coincidence, show to the user that the username and password are invalid.
for (const credential of validCredentials) {
if (credential.username === username.value && credential.password === password.value) {
return window.location.href = '/home';
}
} //end of the loop
alert('Invalid username or password');
}); //end of the callback function
});
On the other hand, in window.location.href = '/home', the string is a malformed URI. You have to send user to a completed URI like, https://google.com/ or http:/yoursite.com/home

JavaScript Login Form Not Validating

Good Evening,
I am trying to create a simple JavaScript login form that will validate by checking only 1 specific email address which has been declared and 1 password that has been declared.
However, no matter what is typed into the fields, even if nothing is present, once the submit button is clicked, the user is directed to the desired page.
I need it to only allow the desired page if the email address and password are the correct. Otherwise, notify them that it is incorrect.
Here is a link to [codepen][1] so you can see the page and script.
https://codepen.io/m0rrisim0/pen/bmzyqj
Any help is appreciated in figuring out why the script is not validating.

You have to use the attribute value from document.getElementById method,
like the following example: document.getElementById("UserName").value
function validate() {
'use strict';
var UserName = document.getElementById('UserName').value;
var email = "adrian#tissue.com";
var Password = document.getElementById('Password').value;
var pass = "welcome1";
if ((UserName == email) && (Password == pass)) {
return true;
} else {
alert("UserName and/or Password Do Not Match");
return false;
}
}
Your form's inputs lack the id atrribute and should return the function on submit event.
<form action="Issues.html" method="post" id="loginform" onsubmit="return validate()">
UserName:
<input type="text" name="UserName" id="UserName">
<br>
<br>
Password:
<input type="password" name="Password" id="Password">
<hr>
<input type="submit" value="Submit">
</form>

Your problem was getElementById(), this function requires a argument and cause a error. Because of this error the line loginform.onsubmit = validate; was never reached so the submit button submit the form without calling a validate function.
There is no need to put this line inside the if statement, but if you want you can change a little bit to getElementById without the parentesis, this way it evaluates to a function that in js is truthy.
You can check a working version of you code here:
if (document && document.getElementById) {
var loginform = document.getElementById('loginform');
loginform.onsubmit = validate;
}
https://codepen.io/francispires/pen/mzvYKX
You can improve this validation

Javascript change password by using an input

I am new in Javascript and I want to make a code where a window will be open asking the user to type a specific password. If the password is correct then he "enters" the page. In the page, he can find an input and a button. He can change the password by filling the input and then pressing the Submit button. Basically to change the value of the variable. The problem is that I don't know how can I "pass" the input with id="changePass" to the variable pass1 and then I am not sure if the new password will be saved. Thank you in advance! Bellow you can find my code:
<html>
<body>
<script>
var entered = false;
var password;
var pass1="pass";
if (entered == false) {
password = prompt('Enter your password in order to view this page!', ' ');
if (password == pass1) {
alert('Correct Password, Enter the Club');
entered = true;
} else {
window.location = "";
}
} else if (entered == true) {
alert('You have already entered the password. Click OK to enter!');
}
</script>
<input id="changePass"/>
<button id="subimt" type"Submit">Submit</button>
</body>
</html>

My friend you can't rely on browser storage and cookies for logging in users and keeping passwords. The least of your problems is that if a user clears his cookies and history you are going to lose it all. :)
This is why I asked if it is a homework or at least something that you don't really care to hold on to user credentials, and your users won't have any problem to re-enter the default password every once a while.
With that being said below is the code you want to store the password to local storage
<input id="changePass"/>
<button id="changePassBtn" type"Button" onclick='changePassBtnClick()'>Change Password</button>
<input id="login"/>
<button id="loginBtn" type"Button" onclick='loginBtnClick()'>Login</button>
<script>
if(!localStorage.getItem('password')){
localStorage.setItem('password', 'pass');
}
function changePassBtnClick(){
localStorage.setItem('password', document.getElementById('changePass').value);
alert('Password changed');
}
function loginBtnClick(){
if(document.getElementById('login').value == localStorage.getItem('password')){
alert('Correct Login');
}else{
alert('Wrong Password');
}
}
</script>

Javascript OnClick before submit button

Im having an issue getting some bit of code to run before the page submits.
When i change the return value to true to submit the form, the code above doesn't run. The way it is now, the code runs and the page is refreshed. I want to pass a true variable to submit the form Any ideas?
function buildMessageC() {
//Create an ePOS-Print Builder object
var builder = new epson.ePOSBuilder();
//Create a print document
builder.addTextLang('en')
builder.addTextSmooth(true);
builder.addTextFont(builder.FONT_A);
builder.addTextSize(1, 1);
builder.addText(document.getElementById('receipt').textContent);
builder.addFeedLine(1);
builder.addCut(builder.CUT_FEED);
//Acquire the print document
var request = builder.toString();
//Set the end point address
var address = 'http://192.168.1.69/cgi-bin/epos/service.cgi?devid=counter_printer&timeout=10000';
//Create an ePOS-Print object
var epos = new epson.ePOSPrint(address);
//Send the print document
epos.send(request);
return false;
The form button
<sf:form onsubmit="return buildMessageC()">
<input class="addToOrderButton button blue large expand" value="Place Order" name="_eventId_placeOrder" type="submit"/>
</sf:form>
Clarification
function doSubmit(){
buildMessageC();
return false;
} gives me print out and reloads the same page not submiting the form
function doSubmit(){
buildMessageC();
return true;
} doesn't print yet submits the form

How to ensure my confirm checkbox is ticked before allowing submission of my form

Once again the novice JS is back again with a question. I want a confirmation tickbox at the end of my form before allowing the user to send me their details and if it's not ticked then they can't submit the form. I've had a look on here and tried using different examples of coding but I just find it all very confusing after looking at 10 or 20 pages of different code. Here is what I've written so far, from what I can make out my form just skips over my checkbox validation code which is obviously what I don't want to happen:
<head>
<script>
function validate (){
send = document.getElementById("confirm").value;
errors = "";
if (send.checked == false){
errors += "Please tick the checkbox as confirmation your details are correct \n";
} else if (errors == ""){
alert ("Your details are being sent)
} else {
alert(errors);
}
}
</script>
</head>
<body>
<div>
<label for="confirm" class="fixedwidth">Yes I confirm all my details are correct</label>
<input type="checkbox" name="confirm" id="confirm"/>
</div>
<div class="button">
<input type="submit" value="SUBMIT" onclick="validate()"/>
</div>

I would just enable/disable your button based on the checkbox state. Add an ID to your button, (i'll pretend the submit button has an id of btnSubmit)
document.getElementById("confirm").onchange = function() {
document.getElementById("btnSubmit").disabled = !this.checked;
}
Demo: http://jsfiddle.net/tymeJV/hQ8hF/1

you are making send be confirm's value.
send = document.getElementById("confirm").value;
This way send.checked will not work. Because you are trying to get the attribute checked from a value (probably, string).
For the correct use, try this:
send = document.getElementById("confirm");
sendValue = send.value;
sendCheck = send.checked;
Then you can test with
if (sendCheck == false){ //sendCheck evaluate true if checkbox is checked, false if not.
To stop form from submitting, return false; after the error alerts.
Here the complete code - updated to work correctly (considering the <form> tag has id tesForm):
document.getElementById("testForm").onsubmit = function () {
var send = document.getElementById("confirm"),
sendValue = send.value,
sendCheck = send.checked,
errors = "";
//validate checkbox
if (!sendCheck) {
errors += "Please tick the checkbox as confirmation your details are correct \n";
}
//validate other stuff here
//in case you added more error types above
//stacked all errors and in the end, show them
if (errors != "") {
alert(errors);
return false; //if return, below code will not run
}
//passed all validations, then it's ok
alert("Your details are being sent"); // <- had a missing " after sent.
return true; //will submit
}
Fiddle: http://jsfiddle.net/RaphaelDDL/gHNAf/

You don't need javascript to do this. All modern browsers have native form validation built in. If you mark the checkbox as required, the form will not submit unless it is checked.
<form>
<input type="checkbox" required=""/>
<button type="submit">Done</button>
</form>