JavaScript - The language of the web and beyond

• Call it ECMAScript
• Basic syntax
• JS for shell scripting
• In the browser
• Example

• Originally named LiveScript by Brendan Eich (Netscape)
• Standardization finished in June 1997 (First Edition)
• Current standard version is 5.1 (JUne 2011)
• Most browsers support only up to version 3
• Many different dialects exist (but do not worry about them!)

• 2D (e.g. <canvas />) and 3D graphics (e.g. WebGL)
• Real time TCP/IP communication (e.g. WebSockets)
• Multi-Threading (e.g. WebWorker)
• Capturing hardware input like webcam, etc.
• Compiling anything for the web (e.g. flash without any plugin)
• Emulating hardware (NES, PC (!), C64, ...)

→ One of many examples

• It's a dynamic language (everything's var)
• Scope is not given by curly brackets, but functions
• Functions are also just objects
• Standard logical operators perform casts automatically
• New logic operators like === do not cast

• Besides it's in a way C-style - consider

  var a = 2; // Line-comment
  var b = 25.3; /* Block-comment */
  var c = a + b - a / b + a * a - b * b;
  var d = "I am a string!";
  var e = 'I am also a string!';
  var f = d + a; // Works, string + obj = string

• Everything is an object
• There are only a few types built-in

• ECMAScript uses 32-bit for numbers AND

  var a = 10, b = 0, c = -0;
  if(a/b !== a/c)
  	alert('How is it possible?');
  

• Always prefer the literal use, like

  "abc"; //Better than new String("abc");
  [1, 2, 3]; //Better than new Array(1, 2, 3);
  { name: 'Florian', age: 28 }; //Better than new Object();
  /[a-zA-Z]/g; //Better than new RegExp("a-zA-Z", "g");
  

• Easily possible with many (or your own?) implementation
• Most popular choice might be Node.js
• Node.js has been developed to write server-side JavaScript
• Code is compiled using Google's V8 (very fast - but still dynamic)
• Download the tarball from nodejs.org
• Installing npm yields a powerful package manager

• Unpack and build it like

  tar -zxf node-v0.8.15.tar.gz
  cd node-v0.8.15
  ./configure # --prefix=/opt/node
  make
  sudo make install

• Maybe add export PATH=$PATH:/opt/node/bin to ~/.profile

#!/usr/bin/env node
var fs = require('fs'); //include package
if(process.argv.length < 3) { //0 = node, 1 = script, 2 = arg #1
	console.log("You have to specify at least 1 argument.");
} else {
	var fileName = process.argv[2];
	var text = "[ " + process.argv.slice(3).join(' ; ') + " ]";
	fs.writeFileSync(fileName, "Args:\n" + text, 'utf8');
	console.log("The file " + fileName + " has been created.");
}

• Use chmod u+x $fn to execute directly
• Writing to stdout by using console.log()
• Reading from stdin with the process.stdin object
• Execute a shell command via child_process.exec()
• Recommended is require('path') if you use paths
• Integration of C++ programs is possible - read more

• Chroma generates XML files (input and output)
• The browser is pretty good at XML
• Browsers do have JavaScript and JS consoles included
• Much easier to inspect than with grep etc.
• Simple example: Sum of all w_plaq nodes

• All good browsers have a JS console
• JavaScript is required for every web app
• The objects we get from the browser is remarkable
• Possibilities: Requests, graphics, evaluation, ...
• Manipulate open websites (ofc. just locally!)

• Basic object is window
• This object contains a property document
• Includes the nodes
• Query by getElementsByTagName(), getElementById(), ...
• We get back HTMLElement objects
• Can manipulate their properties
• Simple example: change background of Google

• We will use the browser for displaying graphics
• We need several methods (don't worry, I prepared something ...)
• Want it dynamic? If you got some time during Christmas
• Let's start!

• Go this page