I have made a very simple JavaScript script. There is 1 .js file with a lot of code, and in the HTML file there is only 2 lines. The script works fine when I test it on a plain HTML page, but when I try it with WordPress, it doesn't work.

I guess it has something to do with the path to the external .js file (src="js/file.js").

What am I missing? Why isn't my script loading correctly?

Edit: See comment to answer below, I have now added the code to the functions.php, but still not working.

Edit2: This is the code I use in the functions.php:

add_action( 'wp_enqueue_scripts', 'my_enqueue_front_scripts' );
function my_enqueue_front_scripts(){
    wp_enqueue_script( 'my-custom-scripts', get_stylesheet_directory_uri() . '/js/file.js' );
}

And this is the code in my head tag:

<script type="text/javascript"> url_detect.OnBack = function() { window.location.replace("URL.org"); } </script>