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preventDefault() cause problem on validating the form

the code below was written to validate simple html form with JavaScript and preventDefault() method means that if the required fields are empty then stop form submission and display error or otherwise submit the form if the required fields are not empty.
The problem comes when I click the submit button the form isn't working.
Can anyone please help me to solve the problem?
let form = document.getElementById("signUp");
let uname = document.forms["myForm"]["userName"].value;
let uemail = document.forms["myForm"]["userEmail"].value;
function validateForm() {
if (uname == " ") {
alert("Name is Empty");
} else if (uemail == " ") {
alert("Email is Empty");
return false;
}
return true;
}
form.addEventListener("submit", function(e) {
e.preventDefault();
validateForm();
});
<form id="signUp" name="myForm">
Name: <input type="text" name="uname" id="userName">
<br> Email: <input type="email" name="email" id="userEmail">
<button type="submit">sign up</button>
</form>

With e.preventDefault() you say that the form should not be submitted.
So you only want to call if in case the validation returns false.
Besides that, your uname and uemail is set before the form is submitted. So it won't contain the state of the input fields at the time the form is submitted. You have to move them into your validateForm function.
let form = document.getElementById("signUp");
function validateForm() {
let uname = document.forms["myForm"]["userName"].value;
let uemail = document.forms["myForm"]["userEmail"].value;
if (uname == " ") {
alert("Name is Empty");
} else if (uemail == " ") {
alert("Email is Empty");
return false;
}
return true;
}
form.addEventListener("submit", function(e) {
if (!validateForm()) {
e.preventDefault();
}
});
<form id="signUp" name="myForm">
Name: <input type="text" name="uname" id="userName">
<br> Email: <input type="email" name="email" id="userEmail">
<button type="submit">sign up</button>
</form>
And uname == " " does not test if the name is empty. It tests if it consists of one character that is a space. The same is for uemail == " ". You probably looking for uname.trim() == ""
As you need to verify the data on the server anyways. And in some way need to display an error if the validation fails on the server side.
It is often sufficient to rely on the HTML solutions to verify the form data (if the browser support is decent enough even if it is not complete).
Something like this:
.error {
display: none;
}
input:not(:placeholder-shown):invalid +.error {
display: block;
}
<form id="signUp" name="myForm">
Name: <input type="text" name="uname" id="userName" placeholder="Name" pattern="^(?!^ +$)([\w -&]+)$" required>
<div class="error">Name must not be empty</div>
<br> Email: <input type="email" name="email" id="userEmail" placeholder="Email" required>
<div class="error">Email must be valid</div>
<button type="submit">sign up</button>
</form>

const form = document.getElementById("signUp");
form.addEventListener("submit", (e) => {
e.preventDefault();
if(validate()) {
form.submit()
}
});
const validate = () => {
const name = document.querySelector("#userName");
const email = document.querySelector("#email");
let hasError = false;
if(!(name.value && name.value.length > 4)) {
const nameErr = document.querySelector("#user-name-error");
nameErr.textContent = "Name is required";
hasError = true;
}
if(!(name.value && name.value.length > 0)) {
const emailErr = document.querySelector("#user-email-error");
emailErr.textContent = "Email is required";
hasError = true;
}
return !hasError;
};
<form id="signUp" name="myForm">
<div class="form-group">
<label for="userName">Name: </label>
<input type="text" name="uname" id="userName" />
<p id="user-name-error" style="color: red;"></p>
</div>
<div class="form-group">
<label for="userEmail">Email: </label>
<input type="email" name="email" id="email" />
<p id="user-email-error" style="color: red;"></p>
</div>
<button type="submit">sign up</button>
</form>

<form id="signUp" name="myForm">
<div class="form-group">
<label for="userName">Name: </label>
<input type="text" name="uname" id="userName" required minlength="4"/>
</div>
<div class="form-group">
<label for="userEmail">Email: </label>
<input type="email" name="email" id="email" required pattern="[^#]*#[^.]*\..*"/>
</div>
<button type="submit">sign up</button>
</form>
This is an example using only html, it is only for your use case of course if you want to add more complexe validation use javascript

Why the output from javascript just shown for a short period of time?

I am developing a Registration form for my assignment. All things are working but when I click on the submit button, the warning messages on the label are just shown for a very short period of time. I am using eclipse and apache tomacat. here is my code.
JSP Code:
<form method="post">
<h2>Welcome to AP Auctions. Please Enter Bid</h2>
<span id="msg" style="color:red;font-size:25px"></span><br/>
<label id="itemid_l">Item Id:</label> <input type="text" name="itemid" id="itemid"/><br/>
<label id="itemname_l">Item Name:</label> <input type="text" name="itemname" id="itemname"/><br/>
<label id="uname_l">Your Name:</label> <input type="text" name="uname" id="uname"/><br/>
<label id="email_l">Your Email Address:</label> <input type="text" name="email" id="email"/><br/>
<label id="amount_l">Amount Bid:</label> <input type="number" name="amount" id="amount"/><br/>
<label id="autoincrement_l">Auto-increment to match other bidders:</label><input type="checkbox" name="autoincrement" id="autoincrement"><br/>
<input type="submit" value="Submit Bid" onclick="validate()"/>
</form>
Javascript Code:
function validate()
{
var itemid=document.getElementById("itemid").value;
var itemname=document.getElementById("itemname").value;
var uname=document.getElementById("uname").value;
var email=document.getElementById("email").value;
var amount=document.getElementById("amount").value;
var autoincrement=document.getElementById("autoincrement");
var flag=true;
if(itemid.length==0){
flag=false;
document.getElementById("itemid_l").innerHTML="<b>Required field!</b> Item Id: ";
}
if(itemname.length==0){
flag=false;
document.getElementById("itemname_l").innerHTML="<b>Required field!</b> Item Name: ";
}
if(uname.length==0){
flag=false;
document.getElementById("uname_l").innerHTML="<b>Required field!</b> Your Name: ";
}
if(email.length==0){
flag=false;
document.getElementById("email_l").innerHTML="<b>Required field!</b> Your Email Address: ";
}
if(amount.length==0){
flag=false;
document.getElementById("amount_l").innerHTML="<b>Required field!</b> Amount Bid: ";
}
if(!autoincrement.checked){
flag=false;
document.getElementById("autoincrement_l").innerHTML="<b>Required field!</b> Auto-increment to match other bidders:: ";
}
if(flag==true){
alert('Good job!!');
return true;
}
else
{
document.getElementById("msg").innerHTML="Required data is missing. Please fill";
return false;
}
}
Any suggestion will help me a lot..

You can use onsubmit event so that whenever user click on submit button this gets call and if the function validate() return true form will get submitted else it will not submit form .
Demo code :
function validate() {
var itemid = document.getElementById("itemid").value;
var itemname = document.getElementById("itemname").value;
var uname = document.getElementById("uname").value;
var email = document.getElementById("email").value;
var amount = document.getElementById("amount").value;
var autoincrement = document.getElementById("autoincrement");
var flag = true;
if (itemid.length == 0) {
flag = false;
document.getElementById("itemid_l").innerHTML = "<b>Required field!</b> ";
} else {
//if fill remove error any
document.getElementById("itemid_l").innerHTML = ""
}
if (itemname.length == 0) {
flag = false;
document.getElementById("itemname_l").innerHTML = "<b>Required field!</b> ";
} else {
//if fill remove error any
document.getElementById("itemname_l").innerHTML = "";
}
if (uname.length == 0) {
flag = false;
document.getElementById("uname_l").innerHTML = "<b>Required field!</b> ";
} else {
document.getElementById("uname_l").innerHTML = "";
}
if (email.length == 0) {
flag = false;
document.getElementById("email_l").innerHTML = "<b>Required field!</b> ";
} else {
document.getElementById("email_l").innerHTML = "";
}
if (amount.length == 0) {
flag = false;
document.getElementById("amount_l").innerHTML = "<b>Required field!</b>";
} else {
document.getElementById("amount_l").innerHTML = "";
}
if (!autoincrement.checked) {
flag = false;
document.getElementById("autoincrement_l").innerHTML = "<b>Required field!</b>";
} else {
document.getElementById("autoincrement_l").innerHTML = "";
}
if (flag == true) {
document.getElementById("msg").innerHTML = "";
alert('Good job!!');
flag = true; //do true
} else {
document.getElementById("msg").innerHTML = "Required data is missing. Please fill";
flag = false; //do false
}
return flag; //return flag
}
<!--add onsubmit -->
<form method="post" id="forms" onsubmit="return validate()">
<h2>Welcome to AP Auctions. Please Enter Bid</h2>
<span id="msg" style="color:red;font-size:25px"></span><br/>
<!--give id to span instead of label-->
<label> <span id="itemid_l"></span>Item Id:</label> <input type="text" name="itemid" id="itemid" /><br/>
<label><span id="itemname_l"></span>Item Name:</label> <input type="text" name="itemname" id="itemname" /><br/>
<label><span id="uname_l"></span>Your Name:</label> <input type="text" name="uname" id="uname" /><br/>
<label><span id="email_l"></span>Your Email Address:</label> <input type="text" name="email" id="email" /><br/>
<label><span id="amount_l"></span>Amount Bid:</label> <input type="number" name="amount" id="amount" /><br/>
<label><span id="autoincrement_l"></span>Auto-increment to match other bidders:</label><input type="checkbox" name="autoincrement" id="autoincrement"><br/>
<input type="submit" value="Submit Bid" />
</form>
Also , if you just need to check for empty field you can just use required attribute on input tag like below :
<form method="post">
<h2>Welcome to AP Auctions. Please Enter Bid</h2>
<span id="msg" style="color:red;font-size:25px"></span><br/>
<!--added required attribute-->
<label id="itemid_l">Item Id:</label> <input type="text" name="itemid" id="itemid" required/><br/>
<label id="itemname_l">Item Name:</label> <input type="text" name="itemname" id="itemname" required/><br/>
<label id="uname_l">Your Name:</label> <input type="text" name="uname" id="uname" required/><br/>
<label id="email_l">Your Email Address:</label> <input type="text" name="email" id="email" required/><br/>
<label id="amount_l">Amount Bid:</label> <input type="number" name="amount" id="amount"required/><br/>
<label id="autoincrement_l">Auto-increment to match other bidders:</label><input type="checkbox" name="autoincrement" id="autoincrement" required><br/>
<input type="submit" value="Submit Bid"/>
</form>

The onsubmit event handler javascript not working

I have a problem. When I clicked the submit button nothing happens, even when I filled out the username and password with numbers (I don't want the username and password contains any number so I did make the condition for it), there is no alert display. I do not know where the problem comes from? Can you guys help me with this
Note: the reset function works fine
function validateInput() {
var firstName = document.forms["sign_up"]["firstName"];
var lastName = document.forms["sign_up"]["lastName"];
var email = document.forms["sign_up"]["email"];
var reg = /^[a-zA-Z]+$/;
if (firstName.value !== '' || lastName.value !== '' || email.value !== '') {
if (firstName.value.match(reg) && lastName.value.match(reg)) {
alert("Form is submitted");
// return true;
return false; // for the demo, so it doesn't submit
} else {
if (firstName.value.match(reg) === false) {
document.getElementById("error").innerHTML = "Numbers are not allowed in username";
return false;
} else if (lastName.value.match(reg) === false) {
document.getElementById("error").innerHTML = "Numbers are not allowed in password";
return false;
}
}
}
}
function reset() {
document.getElementById("first").innerHTML = "";
document.getElementById("last").innerHTML = "";
document.getElementById("email").innerHTML = "";
}
<form id="sign_up" onsubmit="return validateInput()">
<p id="error"></p>
<label for="firstName">First Name</label>
<input type="text" id="firstName" value="" placeholder="Enter your first name">
<label for="lastName">Last Name</label>
<input type="text" id="lastName" value="" placeholder="Enter your last name">
<label for="email">Email</label>
<input type="email" id="email" value="" placeholder="Enter your email">
<button type="submit">Submit</button>
<button type="button" onclick="reset();">Cancel</button>
</form>

Use the Pattern attribute in input for validation like below
<input type="text" id="firstName" value="" pattern="[^0-9]*" title="Numbers are not allowed" placeholder="Enter your first name">
for more references: https://www.w3schools.com/tags/att_input_pattern.asp
And for reset functionality use reset
<input type="reset" value="reset">
It's better than create a special function for it and it saves your number of lines:-)

First, try to avoid to inline event handlers as they are not rec-emended at all. Also to reset form values you can simply use reset() method on the form.
Also, do not use innerHTML just to set the text of your error. You can use textContent instead which is better fit in your example.
You can use addEventListener with submit event to check for validation on your firstname and lastname.
I have fixed your code and its all working as expected.
Live Working Demo:
let form = document.getElementById("sign_up")
var firstName = document.getElementById("firstName")
var lastName = document.getElementById("lastName")
var email = document.getElementById("email")
var reset = document.getElementById("clearValues")
var reg = /^[a-zA-Z]+$/;
form.addEventListener('submit', function(e) {
e.preventDefault()
if (firstName.value != '' || lastName.value != '' || email.value != '') {
if (firstName.value.match(reg) && lastName.value.match(reg)) {
alert("Form is submitted");
} else if (!firstName.value.match(reg)) {
document.getElementById("error").textContent = "Numbers are not allowed in username";
} else if (!lastName.value.match(reg)) {
document.getElementById("error").textContent = "Numbers are not allowed in password";
}
}
})
reset.addEventListener('click', function(e) {
document.getElementById("sign_up").reset();
})
input {
display:block;
}
<head>
</head>
<body>
<form id="sign_up" action="#">
<p id="error"></p>
<label for="firstName">First Name</label>
<input type="text" id="firstName" value="" placeholder="Enter your first name">
<label for="lastName">Last Name</label>
<input type="text" id="lastName" value="" placeholder="Enter your last name">
<label for="email">Email</label>
<input type="email" id="email" value="" placeholder="Enter your email">
<button type="submit">
Submit
</button>
<button type="button" id="clearValues" onclick="reset();">
Cancel
</button>
</form>
</body>

You don't need to return a function in onsubmit event. This should work fine.
<form id="sign_up" onsubmit="validateInput()">
Reference:
https://www.w3schools.com/jsref/event_onsubmit.asp

when onsubmit event in form only first function is working i want to return all 3 function with true

Ajax code to check email is new or existing
I want all the three function return(checkpass() && check() && validate(this)) to work. Currently only the function checkpass() is working. If I write return(check() && checkpass() && validate(this)), only check() function gets triggered.
function check(){
var uname=document.forms["register_form"]["uname"].value;
var uemail=document.forms["register_form"]["uemail"].value;
var upassword=document.forms["register_form"]["upassword"].value;
var ucpassword=document.forms["register_form"]["ucpassword"].value;
if(uname=="" || uemail=="" || upassword=="" || ucpassword==""){
alert("all fields must be filled out");
return false;
}
}
function checkpass(){
var upass=document.forms["register_form"]["upassword"].value;
var ucpass=document.forms["register_form"]["ucpassword"].value;
if(upass!=ucpass){
alert("Confirm password should be same as password");
return false;
}
if(upass=="" && ucpass==""){
alert("cannot be kept blank");
return false;
}
}
function validate(useremail){
xhttp =new XMLHttpRequest();
xhttp.open("GET","emailvalidate.php?uemail="+useremail,true);
xhttp.send();
xhttp.onreadystatechange=function(){
if (xhttp.readyState == 4) {
if(xhttp.responseText==""){
document.getElementById("alert").innerHTML="cannot be empty";
return false;
}
else if(xhttp.responseText=="OK"){
document.getElementById("alert").innerHTML="<span class='badge badge-pill badge-primary'>welcome new user</span>";
}
else if(xhttp.responseText=="NO"){
document.getElementById("alert").innerHTML="<span class='badge badge-pill badge-primary'>Email Already Exist</span>";
return false;
}
else{
document.getElementById("alert").innerHTML="error happened";
return false;
}
}
};
}
<form method="post" action="register_action.php" id="register_form" name="register_form" onsubmit="return (checkpass() && check() && validate(this));">
<br>
<div class="form-group">
<label for="uname">Name:</label>
<input type="text" class="form-control" id="uname" placeholder="Enter Name " name="uname">
</div>
<div class="form-group">
<label for="uemail">Email id: </label>
<input type="email" class="form-control" id="uemail" placeholder="Enter Email ID" name="uemail"
onkeyup="javascript:validate(this.value)"><br>
<span id="alert"></span>
</div>
<div class="form-group">
<label for="upassword">Enter Password:</label>
<input type="password" class="form-control" id="upassword" placeholder="Set password" name="upassword">
</div>
<div class="form-group">
<label for="ucpassword">Confirm Password:</label>
<input type="password" class="form-control" id="ucpassword" placeholder="Enter password again" name="ucpassword" >
</div>
<button type="submit" class="btn btn-success">Submit</button>
</form>

Why don't you wrap them in a function:
var wrapper = function(){
return checkpass() && check() && validate(this);
}
and then
<form onsubmit="javascript:wrapper()">
Also, you can curry this chain of functions to increase readability but well, the example above must resolve your problem.

Field wise form validation

On submitting an empty form I'm receiving the respective errors but I want to remove the error (when they meet the requirement) as I proceed to the next input. Also can anyone give me a solution to do the same with the help of loops. Only JavaScript solution please.
Here's my JS and HTML code..
function validate() {
var letter = /[a-zA-Z]/;
var number = /[1-9]{1}[0-9]{2}/;
var mail = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+#[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/;
var valid = true;
var firstname = information.first.value;
var lastname = information.last.value;
var address = information.Add.value;
var email = information.Email.value;
var pass = information.Pass.value;
var re_pass = information.Repass.value;
var phone = information.mobile.value;
if (firstname === "" || !letter.test(firstname)) {
document.getElementById("fn").innerHTML = "*Enter your First Name*";
console.log("first");
valid = false;
} else {
document.getElementById("fn").innerHTML = "";
}
if (lastname === "" || !letter.test(lastname)) {
document.getElementById("ln").innerHTML = "*Enter your Last Name*";
console.log("last");
valid = false;
} else {
document.getElementById("ln").innerHTML = "";
}
if (email === "" || !mail.test(email)) {
document.getElementById("mail").innerHTML = "*Enter your Email*";
console.log("mail");
valid = false;
} else {
document.getElementById("mail").innerHTML = "";
}
if (pass === "" || !letter.test(Pass)) {
document.getElementById("pwd").innerHTML = "*Enter your Password*";
console.log("password");
valid = false;
} else {
document.getElementById("pwd").innerHTML = "";
}
if (re_pass === "" || re_pass != pass) {
document.getElementById("repass").innerHTML = "*Password didn't match*";
console.log("reenter");
valid = false;
} else {
document.getElementById("repass").innerHTML = "";
}
if (phone == "" || !number.test(phone)) {
document.getElementById("no").innerHTML = "*Enter your Phone number";
console.log("phone");
valid = false;
} else {
document.getElementById("no").innerHTML = "";
}
return valid;
}
<!DOCTYPE html>
<html>
<head>
<title>information</title>
<link rel="stylesheet" type="text/css" href="info.css">
<script type="text/javascript" src="info.js"></script>
</head>
<body>
<div id="form">
<form action="#" method="POST" onsubmit="return validate()" name="information">
<label>Firstname:</label>
<input type="text" name="firstname" placeholder="Enter your name" id="first" autofocus>
<span id="fn"></span><br><br>
<label>Lastname:</label>
<input type="text" name="lastname" placeholder="Enter last name" id="last">
<span id="ln"></span><br><br>
<label>Address:</label>
<input type="text" name="address" placeholder="Address" id="Add">
<span id="add"></span><br><br>
<label>Email:</label>
<input type="email" name="mail" placeholder="Email" id="Email">
<span id="mail"></span><br><br>
<label>Password:</label>
<input type="password" name="password" placeholder="Password" id="Pass">
<span id="pwd"></span><br><br>
<label>Retype Password:</label>
<input type="password" name="retype" placeholder="Retype password" id="Repass">
<span id="repass"></span><br><br>
<label>Phone:</label>
<input type="text" name="firstname" placeholder="XXXXXXXXXX" id="mobile" maxlength = "10">
<span id="no"></span><br><br>
<input type="submit" name="submit" value="submit">
</form>
</div>
</body>
</html>

Perhaps this?
var letter = /[a-zA-Z]/;
var number = /[1-9]{1}[0-9]{2}/;
var mail = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+#[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/;
function validate() {
var information = document.querySelector("#form>form");
var error = 0;
var firstname = information.first.value;
var lastname = information.last.value;
var address = information.Add.value;
var email = information.Email.value;
var pass = information.Pass.value;
var re_pass = information.Repass.value;
var phone = information.mobile.value;
error += firstname === "" || !letter.test(firstname)
document.getElementById("fn").innerHTML = error?"*Enter your First Name*":"";
error += lastname === "" || !letter.test(lastname)
document.getElementById("ln").innerHTML = error?"*Enter your Last Name*":"";
error += email === "" || !mail.test(email)
document.getElementById("mail").innerHTML = error?"*Enter your Email*":"";
error += pass === "" || !letter.test(Pass)
document.getElementById("pwd").innerHTML = error?"*Enter your Password*":"";
error += re_pass === "" || re_pass !== pass
document.getElementById("repass").innerHTML = error?"*Password didn't match*":"";
error += phone === "" || !number.test(phone)
document.getElementById("no").innerHTML = error ? "*Enter your Phone number":"";
return error>0?false:true;
}
document.querySelector("#form>form").oninput = validate;
document.querySelector("#form>form").onsubmit = validate;
<div id="form">
<form action="#" method="POST" name="information">
<label>Firstname:</label>
<input type="text" name="firstname" placeholder="Enter your name" id="first" autofocus>
<span id="fn"></span><br><br>
<label>Lastname:</label>
<input type="text" name="lastname" placeholder="Enter last name" id="last">
<span id="ln"></span><br><br>
<label>Address:</label>
<input type="text" name="address" placeholder="Address" id="Add">
<span id="add"></span><br><br>
<label>Email:</label>
<input type="email" name="mail" placeholder="Email" id="Email">
<span id="mail"></span><br><br>
<label>Password:</label>
<input type="password" name="password" placeholder="Password" id="Pass">
<span id="pwd"></span><br><br>
<label>Retype Password:</label>
<input type="password" name="retype" placeholder="Retype password" id="Repass">
<span id="repass"></span><br><br>
<label>Phone:</label>
<input type="text" name="firstname" placeholder="XXXXXXXXXX" id="mobile" maxlength="10">
<span id="no"></span><br><br>
<input type="submit" name="mysubmit" value="submit">
</form>
</div>