I know this question was asked many times before, I searched really long for the solution but I couldn'd find one, that's why I'm asking. First: I'm trying to connect my HTML-File to my JavaScript file and that worked pretty well. What I want to do now is to display data from my MySql-DB on my HTML-Site, that's why I'm using PHP. I wanted to start simple, that's why I tried to echo "Hello World". But when I run my site, I don't get only "Hello World", I'm getting the whole PHP-Code. How can I fix that problem?
test.php
<?php
echo 'Hello World';
index.html
<!DOCTYPE html>
<html>
    <head>
        <title>MySite</title>
        <link rel="stylesheet" type="text/css" href="style.css">
        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/3.2.0/jquery.min.js"></script>
    </head>
    <body>
      <input type="text" id="size">
      <button id="saveBtn" value="Click" type="button" >Save</button>
      <script src='test.js'></script>
    </body>
</html>
test.js
window.addEventListener("load", function () {
    $('button#saveBtn').on('click', function () {
        var in= $('input#size').val();
        if (size== '')
            alert("Error");
        else {
            $.post("test.php", { input: size}, function (data, status) {
                alert("data + " : " + status);
            });
        }
    });
});
 
    