auto restarting in crontab

[coreyh@free.fr]

Greetings,

My script for monitoring Node.js app as follows. I put it in crontab for 
auto-check and restart if failure.

#!/bin/bash

# scan the port
nc -z 127.0.0.1 3000

if [ $? -eq 0 ];then
  exit
else
  killall node
  sleep 1
  nohup serve -s  /home/myUsername/workspace/xxx-frontend/build &
fi


I can run the script by manual, but in crontab it won't work. that 
means, when node.js dies, it will not get restarted by this script 
automatically.

Can you give any hints?

Thanks
Corey Hickman