Untitled

<body>
    <form method="post">
        <label>Enter your name</label>
        <input id="myName" type="text" placeholder="Your name here"><br>
        <label>enter your first name</label>
        <input id="myFirstName" type="text" placeholder="Your first name here"><br>
        <input id="myButton" type="button" value="submit">
       </form>
        <p id="mydisplay"></p>
    <script src="script.js"></script>
</body>

function myFunction(){
    var x = document.getElementById("myName").value + "<BR>" + document.getElementById("myFirtName").value ;
    if (x != ""){
        alert("Thank you fill in the fields")
    } else{
        document.getElementById("myDisplay").innerHTML = x;
    }
}

window.addEventListener("click", function () {
    document.getElementById("myButton").addEventListener("click", myFunction);
});