help me!

im have 2 file .js
file 1.js code:
document.write("<script src=2.js></script>")
document.write(f)

file 2.js code:
var f="hello"

im want run 1.js get variable of file 2.js by 3.html but don't run!

code 3.html

<script src=1.js></script>