Node.js - KeynesYouDigIt/Knowledge GitHub Wiki

Why server-side JS?

• Node is fast
• Non-blocking IO
• Uses Google's V8 engine
• One language to rule them all
• Good standard library
• npm

Why not server-side JS?

• You have to think in async
• Has maturity issues
• Callback hell
• JavaScript has quirks

Single-threaded

• Single-threaded has advantages over threaded
• Node has an event loop handling all requests, which it delegates to POSIX async threads
• Restaurant metaphor -> one waiter who just takes orders and delivers food vs. 10 waiters who do everything
• Don’t use node for CPU intensive tasks (video processing).

Node Core

• V8 (the engine)
• Libev: The event loop
• LibEio: Async I/O
• LibUv: Abstraction on libEio, libev, etc
• A standard library

_[this stuff in action] - Case Study::why batching requests is faster than making many individual requests.

Global Node objects:

• process - Running process
• require - Function to require package
• console
  • console object is similar, but different
  • console.error prints to stderr
  • console.trace() to show stack trace
• global
• http - Has to be imported
• No document, window, DOM

Modules:

• var express = require("express");
• Can be a JS file or a JSON file
• If the thing isn't a file, it looks inside for an index.js file.
• Don't have side effects in your modules.
• 4 ways to require:
  • require("fs") - Core module or from node_modules folder
  • require("./something") - For arbitrary files
  • require("../config.json") - For arbitrary files
  • require returns whatever is hanging off of module.exports in that file
• You can immediately invoke modules
• You can export anything (function, object, whatever)

Module Patterns

• Simple Object API
• Hide private variables
• Returning an object literal
• Revealing Module

var MyModule = (function(){
    function hiddenMethod() {
        return "hey";
    }

    return {
        publicMethod: privateMethod
    };
})();

MyModule.privateMethod(); // undefined
MyModule.publicMethod(); // "hey"

• Modules are cached- it's the same object!! Returning just an object is a singleton.
• Object constructor (returns an object with a prototype chain)

npm

• Is the tool, npm
  • Has publishing tools (can include tasks)
• Is the site, https://www.npm.org
• Is the registry (which is not the actual packages, just pointers to them)
• Can be public or private
• Project Metadata is in package.json
  • Create one with npm init
• Setting up npm defaults:
  • npm set init.author.name "Kyle Coberly"
  • npm set init.author.email "[email protected]"
  • npm set init.author.url "www.kylecoberly.com"
• Installing locally
  • npm install package_name to try
  • npm install --save package_name to install production dependency
  • npm install --save-dev package_name to install development dependency
• Installing globally
  • npm install -g package_name
• npm ls, npm -g to list installed packages

Semantic versioning

• ~1, ~1.1 goes for highest minor or patch version
• npm shrinkwrap - Snapshots every version
• npm search - Looks for packages, kind of sucks, use Google
• npm update - Updates registry
• npm rm --save - Deletes a package

Process

• The process object has the environment variables, can kill processes, access the shell, etc.

    process.env; // {
        SHELL: "/bin/zsh",
        USER: "kylecoberly",
        HOME: "/home/kylecoberly",
        PORT: 3000,
        NODE_ENV: "development"
    }

• Get arguments via process.argv
  • Takes the command line as space-delimited tokens
  • Doesn't parse anything
  • Includes node
  • Returns array
• To kill node:
  • process.exit(0) for success
  • process.exit(127) for failure
• To respond to signals:

    process.on("eventName", function(error){
        console.log("error", error);
    });

• POSIX codes from OS: SIGINT, ENONT, EADDRINUSE

http/https module

• Write and handle HTTP/HTTPS requests
• Use package to auto load on change = nodemon, eg- nodemon server.js

var http = require("http");

var server = http.createServer(function handleRequests(request, response){
    response.writeHead(200, {
        "Content-Type": "text/plain",
        "X-My-Thing": "The internet"
    });
    response.end("Hello world!");
});

server.listen(3000, "127.0.0.1", function(){
    console.log("It's up!");
})

child_process Module

• Allows you to create sub-processes.
• spawn is an instance of the ChildProcess class. Close the input stream to allow the spawned process to continue running.

var execute = require("child_process").exec;
var ps = execute("ps aux", function (err, stdout, stderr){
    // Do something
};

    var spawn = require("child_process").spawn;
    var someEvent = spawn("someEvent", ["something"]);
    someEvent.stdout.on("data", function(data){
        tee.stdin.write(data);
    };

Standard streams

• STDIN, STDOUT, STDERR
• Event emitters that have standard events. They are pluggable.
  • .data(), .write(), .end(), .pipe()
• Whether it's readable/writeable can depend on perspective
• STDOUT and STDERR are both blocking. Special streams!
• stream.tty will tell you if the user is using it directly, rather than a program

STDIN

• To listen in on data from stdin, use the data and end events
• data is input fed to the program. This may trigger multiple times.
• end says the you’re done reading. STDIN is paused by default

STDOUT

• write() to write to STDOUT

STDERR

• For logging, usually

Buffers

• Buffers are chunks of binary data in memory
• For larger data sets or if you don’t how much of something you'll have:
  • buffer = new Buffer(26); buffer.toString("utf8", 0, 5);

Filesystem IO

• File handling can/should be non-blocking. That's what makes it "web scalable".
• Check that it exists before you start reading
• Don't respond with errors for files that users don't have permissions to access

fs

• File system is core module
• Race conditions = When something is no longer true after you check it
• Don’t use the sync version of the fs methods! Won’t scale!

fs.readFile("file/path", {options}, function(error, contents){
    if (error){
        // throw...
    }
    console.log(contents);
});

fs Methods

• fs.writeFile();
• fs.appendFile();
• fs.exists();
• fs.stats.isFile()
• fs.stats.isDirectory()
• fs.stats.isSocket()
• fs.stats.size
• fs.stats.mtime
• fs.link(“src”, “dest”, “file” callback);
• fs.unlink(); // delete
• fs.mkdir();
• fs.readdir();
• fs.rmdir();

Sync vs. Async

• process.nextTick();
• All async functions require callbacks.
• Callback hell - fight with event emitters, named functions, library, or promises
  • callback and next mean the same thing
• Event emitter is a string with a corresponding callback
  • Events are an imported module
  • Can also inherit from util.
  • emitter.listeners(eventName)
  • emitter.on(eventName, listener)
  • emitter.once(eventName, listener)
  • emitter.removeListener(eventName, listener);

Connecting to Databases

• Install driver module
• Create a connection
• Connect it
• Query it

Connecting to Mongo

• Require MongoClient
• Declare URL
• Connect with mongo
• MongoLab = free cloud instances

Scaling

Vertical scaling (within server)

• Node is fast, but single-threaded. This means every request uses the same process.
• Non-blocking code ensures that something else is handling async requests, usually via callbacks.
• unclustered node app only using one core.
• Clustered node app can use every core.
• cluster module
• Call cluster.fork() once per CPU core
• Strongloop Process Manager does this for you

Horizontal scaling (across servers)

• Scalability is gained by putting a load balancer in front of multiple servers.

Framework Patterns

• KISS Servers: small core, small modules (Node core)
• Convention: follow the leader, steep learning curve (Express, restify, Total.js)
• Configuration: open path, manual effort for advanced (Hapi, Kraken)
• ORM & Isomorphic: model-driven, shared code, steep learning (Loopback, Sails, Meteor)

Server-side Events

• One way, part of HTML5
• EventSource
• Add event listeners in your code
• Two newlines is “end of message”
• Don’t close the connection
• Accept-Type: Event-Stream

Debugging

• DEBUG library
• built-in debugger
• Node Inspector = Chome dev tools for node. Use Chrome debugger, etc.