profile.js has been edited behind the scenes.

You are correct that these additional lines of code are not addressed in this course, and this has been brought up before.

You can find the documentation on util on this page, and the documentation for EventEmitter on this one.

I'll try to do a short explanation of my understanding here, and hopefully someone will correct me if I miss something.

util.inherits() is used here to inherit the prototype methods from EventEmitter into Profile.

At this point, it gets a little bit trickier to follow.

When EventEmitter is called in the Profile instance creation, it appends properties from the EventEmitter constructor to Profile.

// Try using these console.log statements to see what's happening.
console.log(this);
EventEmitter.call(this);
console.log(this);

After that the profileEmitter.emit() method is used to trigger events, passing arguments to listener functions. This lets us handle things like incoming data chunks and errors.

// Triggers an event that adds the data chunk that was just received to body.
profileEmitter.emit("data", chunk);

// Sends an error event, along with the error from catch.
profileEmitter.emit("error", error);

Hopefully that helps explain the changes to the profile.js file, but let me know if you still have questions. Happy coding! :)

Yep it's a different profile.js file, with an example of it's usage. Think of it as a 3rd party library or a black box where only the interface (the external API) is exposed to you. If you notice it's got a similar interface to the http client for retrieving data, so I wanted there to be some familiarity with it's API for asynchronous data calls. For more explanation look here.