How do you install Express module into a Cloud9 project?

Select the Run Panel to set the run configurations as follows:

   name: express 
   path: node_modules/express/bin/express 
   cmd line args: ./your-app-name

Just remember to double click the express line item in the run panel after you have entered the command information.

Cloud9 IDE has some temporary locks on the run functionality within the IDE. If you attempt to open the run panel, and the fields are disabled then follow the following steps:

1. Open the Project Files Panel
2. Drill into the node_modules\express\bin directory
3. rename the express file to express.js
4. Open the file you just renamed by double clicking it.
5. Now open the run pane, and everything but the command line args will be pre-populated for you.
6. Last, enter the app path you want (I.E. ./your-app-name)

There are some additional steps, such as setting up dependencies, that I have covered in greater detail here:

Express Node To the Cloud

Hope this helps those who were seeing the same strange issues I was!

You can install Express using the following in the Cloud9 terminal at the bottom of the Cloud9 IDE:

npm install express

and a simple hello world app that works on Cloud9 is:

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

app.get('/', function(req, res){
  res.send('hello world');
});

// Note: Uses the CLOUD9 port
app.listen(process.env.PORT);

As listed on the Features page on the Cloud9 site itself, the IDE now supports installing express through npm, and running express just like on your own machine.