Can’t prevent client side submission php

I’ve created a register page using php, and the the form successfully sends data to the database.

I’m trying to prevent client side submission, but I can’t get the form to stop submitting, even with nothing in the input fields.

It also submits every time and I refresh the page, and I’m not sure why.

I tried to temporarily removing the php, but I’m still having the same issue.

Before I do any further form validation, I need to the form to stop submitting.

<?php
require_once "connection.php";

session_start();  //intiate session for current user on site 

if (isset($_SESSION["email"]) && isset($_SESSION["password"])) {
    header("location: index.php");
}

$email = filter_input(INPUT_POST, "email", FILTER_SANITIZE_STRING);
$password = filter_input(INPUT_POST, "password");

$hashed_password = password_hash($password, PASSWORD_DEFAULT);

//database entry
$create_account = $pdo->prepare("INSERT INTO users (email,password) VALUES (:email, :password)");
$create_account->bindParam(':email', $email);
$create_account->bindParam(':password', $hashed_password);
$create_account->execute();
?>

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Food Roulette</title>
    <link rel="stylesheet" href="style.css">

</head>

<body class="colorThis">

    <div class="oneForm">
        <form action="register.php" id="signupForm" method="POST">
            <h1 class="register"> Register now </h1><br>
            <label class="emailOne" for="email"> Email Address </label><br>
            <input type="email" id="email" name="email"><br>

            <label class="passwordOne" for="password"> Password </label><br>
            <input type="password" id="password" name="password"><br>
            <button onsubmit="validateRegistrationForm()" class="registerBtn" name="register_button">Login</button>
        </form>
    </div>


    <script src="app.js"></script>
</body>

</html>

App.js with form validation

function validateRegistrationForm() {
    const email = document.getElementById(email);
    const password = document.getElementById(password);

    form.addEventListener("submit", (e) => {
        e.preventDefault();

    })

}

Answer

You are registering event listener after the form has been submitted through onsubmit="validateRegistrationForm()". You should add event listener outside the validateRegistrationForm function. Like this:

    var form  = document.getElementById('signupForm');
    form.addEventListener("submit", (e) =>{
        const email = document.getElementById(email);
        const password = document.getElementById(password);
        e.preventDefault();
    })

and remove onsubmit from button:

   <button  class="registerBtn" name="register_button"> Login </button>

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Answer