Media upload on Meta boxes

Hi,

I’m setting up a meta box with an image uploader following Alex’s example at Theme Foundation: https://themefoundation.com/wordpress-meta-boxes-guide/

However, the upload button isn’t working as nothing happens when clicking on the button.

I’ve checked the source code and I’ve noticed the .js file is missing. Please, may someone have a look to see what I’m doing wrong?

This is my functions.php file: https://snipt.org/zjmj8

And this is /js/meta-images.js file: https://snipt.org/zjnb3

Thanks!