This document provides an introduction to ReactJS, including what ReactJS is, its key features like the virtual DOM and JSX, and how to get started with ReactJS. It was created by Facebook to address performance issues with heavy DOM manipulation. The document discusses ReactJS's use of a virtual DOM for efficient re-rendering, JSX for mixing HTML into JavaScript, resources for learning ReactJS, and ways to set up a ReactJS environment including common build tools. It also briefly describes an example company that uses ReactJS for mobile payments and is hiring developers.

1. Introduction to ReactJS

2. Introduction to ReactJS -
agenda
• What’s the fuss about React
• Where should I start
• Some coding
• Q&A

3. ReactJS is
Facebook’s
child
Mark Zuckerberg: Our
Biggest Mistake Was Betting
Too Much On HTML5 -
September 2012.
This was related to poor
performance at that time.

4. Features
• Virtual DOM
• JSX
• Server side rendering

5. Virtual dom - why React is so
quick
• Direct dom manipulation is
expensive and it’s possible to
do unnecessary manipulations
in transitional states
• React has it’s own tree and
after state changes it
calculates minimal and final
DOM modification
• You may even choose not
render some subtrees
selectively
(shouldComponentUpdate)

6. JSX - why new javascript
flavour?
• JSX makes html native part of
javascript
• For some mixing languages
makes it controversial
• Until you realise that you want
to separate concerns not
technologies
• It is not a new idea (QML,
MXML)

7. Getting started
• Pretty good resources from creators @ http://
facebook.github.io/react/
• Really good community @ http://
www.reddit.com/r/reactjs
• Several Yeoman generators

8. Wiring up
• runtime - JSXTransformer
• grunt-react
• gulp-react
• webpack
• browserify
• …

9. Let’s code

10. Seamless
• Swedish company with development moving
entirely to Łódź
• Currently developing SEQR - mobile payment
platform. This year we are rolling out to many
European countries and USA
• We are hiring: backend (fullstack) developers,
QA engineers,UX, mobile developers,
sysadmins

11. Q&A