how to reflect a code dynamically in static page

Hope you all are doing great!!

I want to display any code (like javascript code for SEO purpose) dynamically in  all static page.

I mean that whenever we put a javascript code dynamically from single master page(From admin panel) it should display globally in all static page(like meta data).

Please help me how to define the code globally once, So that it can be displayed in all static page.......please help me its very urgent .

Thank you