Building

High Performance React Applications

slides.com/joekarlsson | @joekarlsson1

I am
Joe Karlsson

​@JoeKarlsson1

@JoeKarlsson

joekarlsson.com

Software Engineer

How is this going to work?

Why?

My sites are fast enough...

- no one ever

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

Subtitle

Source: https://www.bbc.com/news/technology-34465270

+100ms delay

-1% Amazon’s sales

Source: http://glinden.blogspot.com/2006/11/marissa-mayer-at-web-20.html

2015

$1,070,000,000

Optimizing
on the client

  • Simpler than optimizing on the server

  • You see immediate results

  • More "bang for your buck"

SO YOU WANNA GO FAST?

Why Is
React so
dang fast?

Virtual DOM

  1. Change = entire UI re-rendered in Virtual DOM
     

  2. DOM Diff-ing
     

  3. Real DOM "patched"

Short Answer

ONLY RENDER WHEN  YOU REALLY NEED TO

Long Answer

How To Measure Performance

Use built-in

react_perf tools

34 ms

Use

🔑 Key 🔑

Correctly

The key is used to uniquely identify an element

NEVER USE

Math.random()

or

index during a map(element, index) 

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>;
  }
};

Manage

shouldComponentUpdate

Specify

exactly when a component should render 

class Item extends Component {

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

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

Extend
✨PureComponent✨ instead of
🐢Component🐢

Does a

shallow comparison of all props/state

Will only render
if props/state change

class Item extends PureComponent {

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

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Before you go
all in on PureComponent ...

Use

🔒 Immutable 🔒

Data

Fancy 🎩 word for making a new copy of a object

Immutability makes tracking changes cheap.

const x = { foo: 'bar' };
const y = x;
y.foo = 'baz';
x === y; // true

WTF???

const SomeRecord = Immutable.Record({ foo: null });
const x = new SomeRecord({ foo: 'bar' });
const y = x.set('foo', 'baz');
const z = x.set('foo', 'bar');
x === y; // false
x === z; // true

Build For

⚡️ Production ⚡️

Using

 

renders ~2–8x faster than the development build

NODE_ENV = 'production'

What about Stateless Components?

More thoughts on performance

gzip all the plaintext

gzip            on;
gzip_min_length 1000;
gzip_proxied    expired 
                no-cache 
                no-store 
                private 
                auth;
gzip_types      text/plain 
                application/xml
                application/json;
Accept-Encoding: gzip, deflate
Content-Encoding: gzip

What about images?

png, lossless, everyone uses it

Don't immediately use
progress indicators

User perception: "This is slow"

Source: http://sighci.org/uploads/published_papers/bit04/BIT_Nah.pdf

HTTP/2

Analyze your webpack bundle 🔬

Webpack Bundle Analyzer NPM Repo

Profile your app often 🏃

ONLY RENDER WHEN  YOU REALLY NEED TO

Make it work,
then make it fast

  1. Use key 🗝 correctly

  2. Manage shouldComponentUpdate

  3. Extend ✨PureComponent ✨

  4. Use Immutable Data 🔒

  5. Build for production ⚡️

  1. Analyze webpack bundle 🔬

  2. Profile often 🏃💨

  3. Render when really needed

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

​@JoeKarlsson1

@JoeKarlsson

joekarlsson.com

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