Answers for "how to link an external javascript file"

kill all ports mac

lsof -n -i TCP:8080
COMMAND   PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node     54762   user   23u  IPv4 XXXXXXXXX      0t0  TCP 127.0.0.1:http-alt (LISTEN)
PID // is second field in the response . Then, kill that process:

kill -9 54762 // here put PID number found on the table 54762

killing a port mac

sudo lsof -i :3000

import js in html

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

linking a script .js

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

how to include external javascript in html

<script src="script.js">

Adding external JavaScript to HTML

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