Building

High Performance React Applications

slides.com/joekarlsson | @joekarlsson1

I am
Joe Karlsson

Software Engineer

Why?

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My sites are fast enough...

- no one ever

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40% of users abandon an article if it doesn't load after six seconds

- Danny Bernstein, Google

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+100ms delay

-1% Amazon’s sales

2015

$1,070,000,000

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Optimizing
on the client

  • Simpler than optimizing on the server

  • You see immediate results

  • More "bang for your buck"

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SO YOU WANNA GO FAST?

Short Answer

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ONLY RENDER WHEN  YOU REALLY NEED TO

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Long Answer

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How To Measure Performance

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Use built-in

react_perf tools

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34 ms

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Use

🔑 Key 🔑

Correctly

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The key is used to uniquely identify an element

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NEVER USE

Math.random()

or

index during a map(element, index)

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class List extends Component {
  render() {
    const itemNode = this.props.posts.map((item, idx) => {
      return <Item post={ item } key={ Math.random() } />;
    })
    return <div>{ itemNode }</div>;
  }
};
class List extends Component {
  render() {
    const itemNode = this.props.posts.map((item, idx) => {
      return <Item post={ item } key={ idx } />;
    })
    return <div>{ itemNode }</div>;
  }
};

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Manage

shouldComponentUpdate

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Specify

exactly when a component should render

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class Item extends Component {

  shouldComponentUpdate(nextProps, nextState) {
    if (this.props.title !== nextProps.title) {
       return true;
    }
    return false;
  }

  render() {
    return <h3>{ this.props.title }</h3>
  }
};

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Extend
✨PureComponent✨ instead of
🐢Component🐢

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Does a

shallow comparison of all props/state

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Will only render
if props/state change

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class Item extends PureComponent {

  render() {
    return <h3>{ this.props.title }</h3>
  }
};

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Before you go
all in on PureComponent ...

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Use

🔒 Immutable 🔒

Data

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Fancy 🎩 word for making a new copy of a object

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Immutability makes tracking changes cheap.

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Build For

⚡️ Production ⚡️

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Using

 

renders ~2–8x faster than the development build

NODE_ENV = 'production'

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What about stateless components?

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More thoughts on performance

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Analyze your webpack bundle 🔬

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Profile your app often 🏃

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Make it work,
then make it fast

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  1. Use key 🗝 correctly

  2. Manage shouldComponentUpdate

  3. Extend ✨PureComponent ✨

  4. Use Immutable Data 🔒

  5. Build for production ⚡️

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  1. Analyze webpack bundle 🔬

  2. Profile often 🏃💨

  3. Render when really needed

  4. Make it work,
    then make it fast 🏃💨

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Let's Stay In Touch!

Resources:

@joekarlsson1

High Performance React Applications - Web Rebels

By Joe Karlsson

High Performance React Applications - Web Rebels

React is built with performance in mind. But when is React slow? In this talk we’ll discuss common bottlenecks in React and when you might be making your program work harder than it should.

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