Why does it give an error when trying to call a function from another script?

Question

JavaScript

Decided to output the function to another .js file ('script2.js').

When calling a function from 'script.js', it throws an error.

Explain how the browser combines all these js nicknames into one. And how to get rid of this problem?
If anything, the file with the function is connected earlier (!) than the file where this function is called.

Answer 1

in different scopes
Move the function from $().ready() to the global scope.

Answer 2

window.displayUsers = function(){ ... }