Use Env Varaiables

@@ -15,6 +15,7 @@ app.get('/api/courses',(req,res) => {
 	res.send([1,2,3]);
 });
 
-app.listen(3000, ()=> console.log("Listening on port 3000"));
-
+// PORT
+const port = process.env.PORT || 3000;
 
+app.listen(port,()=> console.log(`Listening on port ${port}...`));
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