WordPress enqueue JS, jQuery and other libraries - wordpress-theming

Question

Here’s what I do in an ordinary html file.
<script src="js/jquery-3.3.1.min.js"></script>
<script src="js/popper.min.js"></script>
<script src="js/bootstrap.min.js"></script>
<script src="js/jquery-ui.min.js"></script>
<script src="js/test.js"></script>
Now, I’d like to see this reflected in WordPress. So in my functions.php I do this:
function theme_files(){
wp_enqueue_script('jquery',get_theme_file_uri('js/jquery-3.3.1.slim.min.js'),NULL,'1.0',true);
wp_enqueue_script('popper',get_theme_file_uri('js/popper.min.js'),NULL,'1.0',true);
wp_enqueue_script('bootstrap',get_theme_file_uri('js/bootstrap.min.js'),NULL,'1.0',true);
wp_enqueue_script('ui',get_theme_file_uri('js/jquery-ui.min.js'),NULL,'1.0',true);
wp_enqueue_script('ownJS',get_theme_file_uri('js/scripts.js'), array('jquery'), '1.0',true);
}
add_action('wp_enqueue_scripts','theme_files');
Unfortunately it doesn’t work. I already found out that its not the dependency in my own js (scripts.js). It doen’t matter whether I do NULL or array(‚jquery‘). Also, I tried to only enqueue my own js without the others. Doen’t seem to change a thing.
Suprisingly, when I do alert(’test’); in my scripts.js it does pop up. But when I do
$(„#idOne“).click(function(){
alert(‚hello‘);
});
Nothing happens when I click on the element with the id=„idOne“
Even when I do pure js
function sayHi(){
alert(‚Hi‘);
}
var one = document.getElementByID(‚idOne‘);
one.addEventListener(‚click‘,sayHi, false);
it doesn’t do a thing ether. What do I do wrong?
Thanks!