How can I add script to the page

Questions
1

When I use linked a page,I wan to add a very large script file to the page. is there a way effecient working effeciently?

2

It is highly not recommended. If you really need to do it on page load then you can add it on page init then you can add it using this snippet:

var script = document.createElement('script');
script.src = 'path/to/file.js';
document.head.appendChild(script);