Notes on Node School's Learn You Node command line tutorial for teaching a summer workshop to the incoming Parsons School of Design M.S. Data-Viz class.

• This tutorial will likely also serve as a javascript review to students new to coding so things will need to be taken slowly and explained carefully.
• Cover how to run node interactively on the command line and mess around, similar to how one would with the javascript console in developer tools in a web browser.
• Explain best practices for where to look when Googling things. eg: "mdn regular expressions"

• write “Hello World!” to the console
• covers basic approach of creating a file and running it using Node
• exercise only verifies if you have console.log(“HELLO WORLD”); your output must match exactly!

• covers argv, looping, starting a loop at a number > 0

• Synchronous vs. Asynchronous operations in Javascript

  • explain why this is important & when you might need to use it both in a browser & with Node (have a good latter example?)

• importing modules

  • (explain core / built-in modules vs. 3rd party modules)

• reading documentation

  • learning how to look up the readFile doc in the browser
  • go over how to read code documentation

• naming of variables

  • what good conventions to follow are in JS & programming in general

• using method chaining, ie: you could combine all those methods on one line

• I/O callbacks in JS,
  • Max Ogden’s fast-food analogy for callbacks is a good one: https://github.com/maxogden/art-of-node#callbacks
  • error handling
  • doing your next task only after the first task is completed and all has gone well.

• reading files in a directory
• filtering files by an extension
• concatenating strings, eg: ‘.’ + argv.process[3];
• briefly describe if statements & boolean logic
  • LPTHW has a good explanation
• this time our anonymous function takes two parameters: error & data.
  • Ask students why
• if no error than the first is null & data is a list of files in the directory
• if there’s an error we’ll do an “early return”

Takes exercise 5 and turns it into a module that can be imported. Students must write 2 files.

From the documentation:

These four things are the contract that your module must follow:  
* Export a single function that takes exactly the arguments described.
* Call the callback exactly once with an error or some data as described.
* Don't change anything else, like global variables or stdout.
* Handle all the errors that may occur and pass them to the callback.

• we must make our previous code into a module, what is a module again?
• our module must handle errors and invoke a callback with parameters for error & data
• when we use our module we must pass it the 3 arguments: the directory to search, extension to filter, & a callback function
• the callback must take the two parameters for error and data

Performing an HTTP GET request

• uses the http module’s built in .get() method
• simplified for http.request()
• note that the get method inherits from http in the documentation: file:///usr/local/lib/node_modules/learnyounode/node_apidoc/http.html#http_http_get_options_callback
• the callback returns a “response” object that can be acted on:
  • response.setEncoding(‘utf8’);
  • response.on(‘error’, console.error);
  • response.on(‘data’, console.log);

Questions / Homework:

• What is stdout? Hint: Google "standard streams"
• What’s encoding? Why is it important? What’s utf8? What are other types of encoding?
• What are other types of HTTP requests? What would you use them for? hint: remember the "CRUD" acronym.

• Learning how to "collect" all data before acting on it.
• Can be solved either by collecting data across multiple events or by using a 3rd party module. Go over both ways?
• cover installing 3rd party modules using npm
• Explain the concept of "streaming" data: grabbing chunks until we have the whole thing. Then we do stuff with the data.

• Task: Given three server requests that will take different amounts of time to complete, print the results of each request in the same order the urls are passed to you, without a 3rd party module.
• I used an object to keep track of the data's order, but an indexed array (used in the actual answer) is more elegant / simple.

Questions For Students:

• How do we track Asynchronous tasks?
• And then print their results in the same order that we asked for them?

Task:

  Your server should listen to TCP connections on the port provided by the first argument to your program. For each connection you must write the current date & time in the format:

	"YYYY-MM-DD hh:mm"

  followed by a newline character. Month, day, hour and minute must be zero-filled to 2 integers. For example:

	"2013-07-06 07:42"

• Covers creating a Node TCP server.
• Covers the Date object in Javascript.
• Have the option of using the strftime module to simplify working with dates.
• actual answer demonstrates how to "zero fill" numeric strings:

function zeroFill(i) {
  return (i < 10 ? '0' : '') + i
}

// this method will be easier to explain to students
function zeroFill(x) {
  if (x < 10){
    x = '0' + x;
  } 
  return x;
}

• create an http server
• open a connection to a port
• stream a file's contents to the client
• uses streaming to read the file and send its data to the client
• use the .pipe() method to send the file contents to the response

Objective:

• create an http server that only accepts 'POST' requests
• pipe the output of the request to the response as an uppercase string

Students will learn:

• the concept of mapping. Mention Array.map() in JS and show an example. MDN has good documentation.
• re-iterating the concept of piping input and output
• filtering for request types and providing an

Objective:

• create an HTTP server that serves JSON data to the client based on the requested URL

Students will learn:

• What the hell is Unix time?
• How do we deal with date-time data in JS?
• What is JSON data & how to we work with it?
  • eg: creating it, parsing it, stringifying it
• What is routing?
• How do we parse a URL string in Node (via the url core-module)?
• What is a query string?
• What is a regular expression and how are they useful?

Tips & Tricks:

• search for "url" in the response object using grep:
  learnyounode run ex13.js | grep --line-buffered "url"
• using regular expressions in JS to search strings. MDN documentation on RE