Answers for "script which will insert code in html file"

kill app at port

#To list any process listening to the port 8080:
lsof -i:8080

#To kill any process listening to the port 8080:
kill $(lsof -t -i:8080)

#or more violently:
kill -9 $(lsof -t -i:8080)

kill port

sudo kill -9 `sudo lsof -t -i:9001`

include script in html

<script type="text/javascript" src="/path/to/script.js"></script>

how to link javascript to html

<script src = "index.js"></script>