What is React.js

Javascript library for User Interfaces

  • Open Source
  • Built by Facebook
  • Just a View
  • High Speed Virtual DOM
  • Uses JSX Syntax

Why is React so fast?

  • Reading and writing to the document object model (DOM) is slow
  • JS Objects faster that the DOM
  • React only reads from the virtual DOM
  • React only writes to the real DOM
  • No polling, when rendering only necessary changes are sent to the real DOM

Developer Tools

  • react-detector - lets you know when react is there
  • react-developer-tools - check react elements
    • ctrl + optn + j / ctrl + shift + j

Add the React library in Head

<script src=""></script>

Rendering content

<script> React.render(React.createElement('div', null, 'Hello World!'), document.body); </script>

JSX: Javascript as XML

Need the JSX Transformer

Converts JSX to pure javascript

<script src=""></script>

Example of JSX:

var HelloWorld = React.createClass({ //Render is required for every react component render: function(){ return ( **<div> <h1>Hello World</h1> <p>THis is some text</p> </div>** ); } });

React.render(, document.body); ```

Precompiling JSX

Better to precompile the JSX as it ill currently do it at run time. Slowing down the app.

Install React tools module

sudo npm install -g react-tools

Runnning the precompiler

jsx src/ build No longer need the transformer, just need a link to the built js.

What is a React Component?

  • Composable: a collection of components make up a page
  • Reusable

A component is a class from createClass

To reuse the component just render the tag, but make sure it is wrapped in a div


Giving components attributes, similar to html attributes

In component use:

<MyComponent text="hello world"/>

In component declaration:

render: function(){ return <div> <h1>{this.props.text}</h1> <p></p> </div>; }

this.props means

Children Property

<MyComponent text="hello world"> Yo yo yo </MyComponent>

You can use the content of the react component with:


Handling Events

Add events to the component

var Note = React.createClass({ <b>edit: function(){ alert('editing note'); }, remove: function(){ alert('removing note'); },</b> render: function() { return ( <div className="note"> <p>{this.props.children}</p> <span> <button **onClick={this.edit}**/> <button **onClick={this.remove}** /> </span> </div> ); } });


When state changes of a component it is Render is called again

Setting Initial state

getInitialState: function(){ return {var: false} },

Setting State

Use: this.setState()

Primary method to trigger use interface updates from event handlers

Changing State

this.setState({checked: !this.state.checked})

Accessing State



Access the properties of a DOM node

Also flow data to a chid component

Setting References

<input ref="myText" type="text"/>

Accessing References

var val = this.refs.myText.getDOMNode().value;


propTypes: { .. }

  • Part of the React library used to handle validations
  • Usually a ECMAScipt Object


propTypes: { count: function(props, propName){ if (typeof props[propName] !== "number"){ return new Error("The count property must be a Number "); } if (props[propName] > 100){ return new Error("Creating " + props[propName] + " notes is ridiculous"); } } },

Child components can inherit state and props


To ensure the state and identity of our components is maintain throughout multiple renders we need to assign a unique key to components:

}, eachNote: function(note, i){ return( <Note key={} index={i} onChange={this.update} onRemove={this.remove} >{note.note}</Note> ); },

Component Lifecycle

Times of change of state during component lifetime

React provide hooks for creation, lifetime and tearDown


Called once: getDefaultProps getInitialState

Called Just before Render: componentWillMount

Required Method: render

After Successful Render: componentDidMount


componentWillReceieveProps shoudlComponentUpdate componentWillUpdate render componentDidUpdate


componentWillUnmount: Just before Unmounting

Best Practices

It is React best practise to have all Components in seperate files

Note: That means that compents need to be referenced before the React.render() file [Main.js]

Frameworks for React

  • Browserify
  • Reactify
  • Webpack
  • Grunt
  • Gulp

Things to Check out

  • React Native
  • flow
  • react-TestUtils
  • Jest