Intro To React

What is react?

- how does it differ from a framework?

Change Detection

Comparison of the big 3

AngularJS

React

Angular

Dirty Checking

const dirtyCheck = (lastState, newState) => deepEqualCheck(lastState, newState)

$digest.onDigest((components) => {
  components
    .filter(dirtyCheck)
    .forEach((oldState, newState, component) => component.render(newState))
})

$digest.run() // runs over and over and over thousands of times in milliseconds

When Does it check?

- DOM Events

- Parent Component Changed

- Component props changed (html attributes)

Zone Change Detection

When Does it check?

- Zone changes (events)

const components = angularComponents() // List of angular components

components.forEach(component => {
  component.onMarkedForChange((component) => {
    component.root.children.forEach(component => component.update())
  })
})

- Parents updated

Virtual Dom Diff

When Does it check?

- Component Changed (class props)

- Parent Component Changed

- Component props changed (html attributes)

whenShouldCheckForChange((oldComponent, newComponent) => {
  const renderedOld = render(oldComponent),
        renderedNew = render(newComponent)

  if (isDifferent(renderedOld, renederedNew))
    updateDom(newComponent.element, renderedOld)
})

How to create a react component

class MyComponent extends React.Component {
  prop = 'World'

  render() {
    // Notice className instead of class
    return <span className='test'>Hello {this.prop}<span>
  }
}

ReactDOM.render(
  <MyComponent/>, 
  document.getElementById('react-view-container')
)

JSX

- It's mostly HTML with a few differences

- Major difference is className because class is reserved

const ComponentTemplate = () => <div onClick={this.onClick}>
  <img src={this.imageUrl}>
  <span>{this.imageTitle}</span>
</div

const MajorComponent = () => (<div>
  <ComponentTemplate/>
</div>)

Conditional Rendering

// Conditional Rendering Way 1

const HelloComponent = (props) => (<div>
  {props.isMorning ? <GoodMorning/> : <Hello/>}
</div>)


// Or in a class

class HelloComponent extends React.Component {
  render() {
    const Greeting = this.pros.isMorning ? <GoodMorning/> : <Hello/>

    return (<div>
      <Greeting/>
      {this.someProp && <GoodMorning/>}
    </div>)
  } 
}

// Stop component from rendering

const GoodNightComponent = (props) => {
  if (true)
    return null // Will prevent rendering

  return ...
}

Lists

class HelloComponent extends React.Component {
  const data = [{id: 1}, {id: 2}, {id: 3}]

  render() {
    const greetings = R.map((a) => <span key={a.id}>a.id</span>, data)

    return (<div>
      {greetings}
    </div>)
  } 
}

Lifecycle

Validating and Type Checking Component Props

class MyComponent extends React.Component {
  static propTypes = {
    myArray: React.PropTypes.array,
    customArray: React.PropTypes.oneOf([1, 2, 3]),
    customObject: React.Proptypes.shape({
      name: React.PropTypes.string,
      number: React.PropTypes.number
    })
  }
}

How Components Decide to Update

class MyComponent extends React.Component {
  componentShouldUpdate() {
    return true // defaults to this
  }
}

class MyComponent extends React.PureComponent {
  shouldComponentUpdate() {
    return shallowPropDiffCheck(this) // not actual code
  }
}

Ramda and React

const ComponentTrue = R.always(<TrueComponent/>)
const ComponentFalse = R.always(<FalseComponent/>)

const chooseComponent = R.ifElse(isTrue, ComponentTrue, ComponentFalse)

compose(chooseComponent, convertToBoolean)

Wrapping Up

- Don't Use Inheritance

- Be functional (pure functions are useful)

- Lift shared needs to parent components