how to call function from one js to other js

Question

i have n no of js file say 1.js, 2.js,  3.js .......

 

all the three js contains one function say

function hello()

{

 alert("In js file 1/2/3/...n");   // as and in which js

}

 

now i have another js file say x

in x we have var id and from somewhere i am getting id value

if id=1 the hello function of js1 should be called    and alert button should popup In js file 1

if id=2 the hello function of js1 should be called   and alert button should popup In js file 2

....

....

if id=15 the hello function of js15 should be called  and alert button should popup In js file 15

if id=n the hello function of js'n' should be called  and alert button should popup In js file n

 

how can this be done. any suggestion