Forever detected script exited with code: 0

I have a app4.js with content:

var express = require('express');
var app = express();

app.get('/', function (req, res) {
  res.send('Hello World!');
});

app.listen(3000, function () {
  console.log('Example app listening on port 3000!');
});

I'm on Win10 cmd, I can success run it with node app4.js and get Example app listening on port 3000!,

but when I use forever -a forever.log start app4.js, it show error

Forever detected script exited with code: 0

Where is the problem? How to solve it?

Cmd Message:

D:\app>node app4.js
Example app listening on port 3000!
^C
D:\app>forever -a forever.log start app4.js
warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
error: Forever detected script exited with code: 0

Another Answer say it's related to ./bin/www, but I can't understand what does it mean.

Solution

After some try I got it, here's my complete tring process:

1.In the beginning, I'm watching this video to learn forever, and at 10:24 it use forever start server.js and successfully run the server file.

2.Theoretically if I use forever start app4.js it should success, but I got error:

D:\app>forever start app4.js
warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
info:    Forever processing file: app4.js
error:   Cannot start forever
error:   log file C:\Users\admin\.forever\forever.log exists. Use the -a or --append option to append log.

3.By the message, I think I should use -a to append log to some file, so I create a log file forever2.log under current folder, and use forever -a forever2.log start app4.js, the I got the error:

error: Forever detected script exited with code: 0

4.After some try, suddenly I look carefully to the nodejs book I'm reading, its example is forever start -l forever.log -o out.log -e err.log app.js, that is the -x is put between start and app.js, so I changed the command to forever start -a forever2.log app4.js and got

warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
info:    Forever processing file: forever2.log

That is it's processing forever2.log, but what I want is app4.js

5.Finally I try forever start -a app4.js, and I got

warn:    --minUptime not set. Defaulting to: 1000ms
warn:    --spinSleepTime not set. Your script will exit if it does not stay up for at least 1000ms
info:    Forever processing file: app4.js

Then I run Browser at http://localhost:3000/, the Hello World! finally show!