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Node.js Essential Training
Illustration by Richard Downs

Supplying middleware to modify HTTP response headers


From:

Node.js Essential Training

with Joseph LeBlanc

Video: Supplying middleware to modify HTTP response headers

When you're building out an express application, usually you're handling one request at a time. However, there's some instances where there's logic applying to all requests. In this video, we'll write some Express middle ware for all requests. Go to the Exercise Files and go to chapter five, video five and then copy the Start folder to the Desktop. Now let's go to terminal and install the modules. Type in cd and space and then I'm just going to drag the folder into terminal to get this path.
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  1. 3m 9s
    1. Welcome
      42s
    2. What you should know before watching this course
      57s
    3. Using the exercise files
      47s
    4. Using the challenges
      43s
  2. 18m 50s
    1. Why use Node.js?
      2m 1s
    2. Choosing a Node.js installation process
      4m 56s
    3. Installing Node.js on the Mac
      2m 5s
    4. Installing Node.js on Windows
      1m 43s
    5. Installing Node.js via Node Version Manager on Ubuntu Linux
      4m 45s
    6. Installing Node.js via Node Version Manager on a Mac
      3m 20s
  3. 13m 54s
    1. Exploring language additions to the V8 JavaScript engine
      3m 38s
    2. Understanding require() and modules
      6m 39s
    3. Understanding callback execution in the event loop
      3m 37s
  4. 12m 23s
    1. Initializing Node.js projects
      2m 37s
    2. Finding an NPM
      3m 30s
    3. Maintaining projects using the npm command
      6m 16s
  5. 21m 4s
    1. Creating modules with getters and setters
      6m 33s
    2. Understanding module caching and scopes
      6m 15s
    3. Implementing JavaScript creational patterns
      5m 8s
    4. Challenge: Leveraging module caching
      55s
    5. Solution: Leveraging module caching
      2m 13s
  6. 32m 27s
    1. Starting Express applications
      3m 42s
    2. Handling GET requests returning JSON
      3m 26s
    3. Navigating large datasets using request variables in routes
      5m 4s
    4. Modifying data through PUT requests
      4m 32s
    5. Supplying middleware to modify HTTP response headers
      4m 37s
    6. Generating HTML views in Jade
      8m 9s
    7. Challenge: List all records as JSON
      37s
    8. Solution: List all records as JSON
      2m 20s
  7. 25m 37s
    1. Evaluating unit testing methodologies
      3m 8s
    2. Isolating existing code for testing
      6m 47s
    3. Supplying helpers for test data
      2m 35s
    4. Writing unit tests with Mocha
      6m 5s
    5. Simulating HTTP requests with SuperTest
      7m 2s
  8. 28m 45s
    1. Connecting to MongoDB via Mongoose
      4m 16s
    2. Defining schemas for collections in Mongoose
      3m 47s
    3. Querying MongoDB collections
      5m 32s
    4. Persisting Express sessions through MongoDB and mongo-connect
      7m 6s
    5. Logging in to Express applications using Passport
      8m 4s
  9. 21m 47s
    1. Controlling the built-in REPL
      4m 18s
    2. Constructing a custom REPL
      5m 40s
    3. Receiving command-line arguments with Optimist
      6m 14s
    4. Building command-line tools
      3m 35s
    5. Challenge: Launch a custom REPL from a command
      41s
    6. Solution: Launch a custom REPL from a command
      1m 19s
  10. 15m 46s
    1. Emitting events and attaching listeners
      5m 32s
    2. Streaming chunked data through readable streams
      2m 33s
    3. Controlling readable streams
      1m 52s
    4. Piping readable data into writable streams
      2m 10s
    5. Handling duplex streams over TCP
      3m 39s
  11. 4m 6s
    1. Deploying projects to cloud hosting services
      2m 36s
    2. Finding Node.js resources
      1m 30s

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Node.js Essential Training
3h 17m Intermediate Oct 16, 2013

Viewers: in countries Watching now:

Node.js is a powerful tool for controlling web servers, building applications, and creating event-driven programming. And it brings JavaScript—a language familiar to all web developers—into an environment independent of web browsers. Learn all about Node.js and start creating JavaScript applications in this course with Joseph LeBlanc. He shows how to install Node.js on Mac, Windows, and Linux and dives deep into its modules and Express framework for app development. Learn how to unit test your code, start sessions on web servers, stream data, and create simple command-line tools.

Topics include:
  • Why use Node.js?
  • Installing Node.js
  • Understanding the event loop
  • Initializing Node.js projects
  • Creating modules with getters and setters
  • Starting Express applications
  • Testing your code
  • Working with sessions and databases
  • Building command-line tools
  • Emitting events and attaching listeners
  • Controlling readable streams
Subjects:
Developer Servers Cloud Computing Programming Languages
Software:
JavaScript Node.js
Author:
Joseph LeBlanc

Supplying middleware to modify HTTP response headers

When you're building out an express application, usually you're handling one request at a time. However, there's some instances where there's logic applying to all requests. In this video, we'll write some Express middle ware for all requests. Go to the Exercise Files and go to chapter five, video five and then copy the Start folder to the Desktop. Now let's go to terminal and install the modules. Type in cd and space and then I'm just going to drag the folder into terminal to get this path.

Now I'm going to type npm space install and then enter. Now all the modules are installed and we're ready to go. Let's start up the server and then go to one of our routes. Type in node, space, app. And then hit Return. The server is now listening on port 3000. I'm going to go to Postman. If you don't already have Postman installed, you can get it from the Google Chrome store. We're going to be looking at some HTTP Header information. And that information can also be found in many of the web inspectors with different web browsers.

So you don't necessarily have to use Postman, but I find this one to be the most convenient. There's already a URL entered here and I just want the flight 33 route. And I'm going to switch to the Get method and now I'm going to send this request. Now click on over to the Headers tab. One thing you'll notice, is a Header here called X-Powered-By and the value is currently set to Express. This is a default value that Express sends out, but I'd really like to change this to something else, because I don't necessarily want to broadcast to the world that I'm using the Express framework.

So to do that, we're going to write a small piece of middleware, that'll change this value. Open up the Start folder in Sublime Text or any Text Editor you prefer and then go to App.js. We're going to add the middleware right here in the middle of all these app.use calls. We're going to add our own. So type app.use and then as the argument you're going to pass in a function. This function is going to provide three arguments, request, response and next.

So now I'm going to reset that X-Power-By Header. We're going to type res.set and then the first argument is the Header name. The second argument is the value that we want to assign to that Header. I'm going to call this Flight Tracker. The function I've just written is known as middle ware. It's designed so you can easily add it into your express application. The arguments are important to note, just like HTTP requests, you get the request and response objects passed as arguments.

However, the final argument is a function called next. It's very important to call next. Otherwise the server will never return a response. Calling next tells Express to process the next piece of middleware. So now let's save this file and then go back to terminal. Now, we're currently still running the same code that we started with. And we need to stop the server, so that it reloads. So press ctrl + c and then press up on the keyboard. This will bring up the last Command. And now finally press Return.

And now the server is been restarted. Let's go back to the browser and then click Send again. You'll notice that this response is taking awhile to come back. We may not of coded this quite correctly. I'm going to stop the server and I'm going to go back to the code. So here's the problem with the code. We never called that next function, so it stopped here on line 22. Let's add a line beneath that and call next. Not let's go back to terminal and restart the server.

And now let's go back to the browser and try the request again. So now if we go to the Headers, X-Powered-By is now set to FlightTracker. This should also work for other requests. Let's pull up that put request from the previous video. I'm going to Send it and then the Headers still say Flight Tracker. It should also even work if we do an invalid request. For instance, if I change this URL to info and hit Send, it'll tell me that it can not put info. But if I go to Headers, it'll still show Flight Tracker for X-Powered-By.

When you need to make a change to every request reaching your express application, write middleware. Just be sure to call the next function, otherwise other middleware will never run. In the next video, we'll create some templates for get requests.

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