java for background

hello

i have a javascript to implement multiple randomic background images

usually i apply it to all my pages, so it works in the whole website

now im using wordpress – read somewhere that i need to use template pages to apply javascript to wordpress – how should i proceed to apply the java to a template file to make this script work in my whole wordpress website, in all pages ?

this is my website https://www.connectto.com.br/websites/

this is the java i want to apply to all pages

https://www.connectto.com.br/java-bgrandomico.txt

help please ?

??