Web Programming @ MIPT, 2015-2016

What is node.js?

• General-purpose Javascript based on v8 engine
• Backed by Joyent company
• Appeared in 2009
• Cross-platform

Installation

• Ubuntu: sudo apt-get install nodejs nodejs-legacy
• MacOSX: brew install node
• Windows: choco install nodejs

Example

			console.log("hello, world");
		

Asynchronous execution in node.js

• No threads
• No blocking calls

while (true) {
  process events;
}
		

Example of a blocking call:

			contents = file.read();
			next line will be executed after the file is read
		

Example of a non-blocking call:

			file.read(function(contents) { ... });
			next line will be executed at once, without waiting
		

Globals

• globals - global namespace (mainly used for writing)
• process - current process instance
• console - similar to browsers, logging
• require, module, exports - import system
• setTimeout, setInterval and friends

Events

• EventEmitter - building block of the events machinery

  var EventEmitter = require('events');
  let emitter = new EventEmitter();
  

• emitter.on() adds event handlers
• emitter.emit() triggers events
• emitter.removeListener() - removes event handlers

Buffers

• Buffer is binary data representation
• Buffers have an Array interface, with slice, length, etc.
• Can transform into strings (encoding must be specified)
• Unsigned and signed integers of size 8, 16 and 32 bits and of different endianness can be read and write
• In order to avoid the garbage collection overhead of creating many individually allocated Buffers, by default allocations under 4KB are sliced from a single larger allocated object. This approach improves both performance and memory usage since v8 does not need to track and cleanup as many Persistent objects.

File system

• var fs = require('fs');

• There are asynchronous (by default) and synchronous (*Sync) function versions
• Function names are similar to typical UNIX commands and stdlib.h
• Files can be read and written in streaming mode with events support
• fs.FSWatcher uses inotify / FSEvents mechanisms to deliver file system change events

Exceptions

• All exceptions are instances of Error
• There are a few predefined error classes available
• stack property allows finding the place where the exception was thrown
• Exception handling in asynchronous mode is different than in synchronous mode
• There is a convention of "error" event for pipes

Debugging

• node debug ... allows interactive debugging of the script; alternatively, send SIGUSR1 signal to already running script and use ‑p <PID> switch
• Insert debugger into your script to hit a breakpoint there
• Command syntax is similar to GNU debugger (gdb)
  • bt - print the backtrace
  • c - continue execution, restart - relaunch the script
  • n - step next, s - step in, o - step out
  • watch(expr) - inspect the expression, be notified on changes

Import system

foo.js:

			exports.jack = "the sparrow";
		

bar.js:

			var foo = require("./foo.js");
			console.log(foo.jack);
		

Importing packages

1. Define package.json with main pointing to the actual file to import
2. index.js is probed automatically
3. index.node is probed automatically

Node package manager

• Installed with node.js
• More than 200 000 packages are available
• High code reusability
• Tree node_modules structure (npm v3 is about to change this)
• Reads metadata from package.json

			npm install <name>
			npm uninstall <name>
			npm search <name>
		

package.json

• npm install reads package.json in the current directory and installs dependencies and devDependencies to node_modules in the current directory
• Fields like name, description are used for package export to a repository
• version syntax is very flexible and relies on semver
• bin allows setting CLI entry points
• scripts allows setting local entry points (npm run ...)
• package.json can be created interactively using npm init

Bower package manager

• Specific to frontend
• More than 40 000 packages
• Fetches files to bower_components
• Reads metadata from bower.json

			bower install <name>
			bower uninstall <name>
			bower search <name>
		

Gulp

• Frontend build system
• Similar to make, the build definition is read from gulpfile.js
• Has about 2000 plugins
• Employs a streaming architecture with small memory footprint

Build pipeline story

...
"scripts": {
  "gulp": "gulp"
},
...
			

• Select the desired processing tools
• Find the corresponding Gulp plugins
• Write rules in gulpfile.js and specify devDependencies in package.json
• npm run gulp does the magic

Project idea

Make the same as npm dependency visualization but for Gulp.

Similar: gulp-graph-tasks. We can do better!

Tip: use gulp --tasks-json

Tip: do not bind to Gulp (use independent intermediate representation), so that the code can be reused for other languages (Python, Go, etc.)

Hint: do not forget about d3.js

Next steps

• Pass interactive node.js tutorials: 1, 2, 3
• Watch videos: 1, 2, 3
• Read books: 1, 2, 3
• Download cheatsheet: 1, 2
• Pass Gulp tutorials: 1, 2, 3
• Continue to Frontend frameworks