React Native: Under the Hood

Transcript

1. 1.

   React Native:
 Under the hood Alex Kotliarskyi Facebook

2. 2.

   Plan 1. Why native apps matter? 2. How ReactJS works

   3. Running ReactJS on native platforms
3. 3.

   Why do we
 ❤ 
 native apps?

4. 4.

   Native Apps • Fast, responsive • Complex gestures and smooth

   animations • Consistent with platform
5. 5.

   None
6. 6.

   Building native apps is hard • Different stacks of technologies

   • No knowledge and code sharing • Slow iteration speed • Hard to scale
7. 7.

   Web got this right

8. 8.

   Web • Different stacks of technologies • No knowledge and

   code sharing • Slow iteration speed • Hard to scale HTML / CSS / JS Same code and tech F5 / ⌘R React!
9. 9.

   Web apps on the phone are not great • Very

   hard to provide smooth experiences • Not designed for complex interactions • Impossible to embed native components
10. 10.

    Development experience Awesome
 apps

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    React Native

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    None
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    UI = ƒ*(data) * No side effects

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    None
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    UI = ƒ(count)

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    UI = ƒ(count) =
 div( span('Count ' + count), button('Add

    +1') )
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    render()  {      return  (        

     div(              span(                  'Count:  '  +  b(this.state.count)              ),              button(                  'Add  +1'              )          )      )   }
18. 18.

    render()  {      return  (        

     <div>              <span>                  Count:  <b>{this.state.count}</b>              </span>              <button>                  Add  +1              </button>          </div>      )   } HTML VirtualDOM
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    render()  {      return  (        

     <div>              <span>                  Count:  <b>{this.state.count}</b>              </span>              <button  onClick={()  =>  ???  }>                  Add  +1              </button>          </div>      )   }
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    TextView  text  =  (TextView)findViewByID(R.layout.label);   text.setText('10'); _label.text  =  @"10"; too

    complex Android Objective-C JavaScript document.getElementByID('count').children[1].innerHTML  =  '10';   $('#counter  b').html('10');
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    render()  {      var  count  =  this.state.count;    

     return  (          <div>              <span>                  Count:  <b>{count}</b>              </span>              <button  onClick={()  =>  ???  }>                  Add  +1              </button>          </div>      )   }
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    render()  {      var  count  =  this.state.count;    

     return  (          <div>              <span>                  Count:  <b>{count}</b>              </span>              <button  onClick={()  =>  this.setState({count:  count  +  1})}>                  Add  +1              </button>          </div>      )   } setState
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    setState

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         <div>              <span>

                     Count:  <b>9</b>              </span>              <button>                  Add  +1              </button>          </div>      <div>              <span>                  Count:  <b>10</b>              </span>              <button>                  Add  +1              </button>          </div> state  =  {count:  9} state  =  {count:  10} <b>9</b> <b>9</b> <b>10</b> findDOMNode(b).innerHTML  =  '10';
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    Components Browser DOM UIKit Components Components Components VirtualDOM

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    1. Runtime 2.Base components 3. Calling native functions

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    ECMAScript 5

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    JavaScript Core • Part of WebKit project • Open Source

    • Ships with iOS Runtime
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    <div>   <span>   <img> <View>   <Text>   <Image>

    <ScrollView>   <MapView>   <TabBar>   <DatePicker>   ... Base components
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    create(view, parent, attributes)*
 update(view, attributes) delete(view) * actually React is

    more complex that that
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    Just call native functions? nope

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    Synchronous

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    Native Method JavaScript time Waiting…

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    JavaScript time Native JavaScript Native

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    Synchronous Asynchronous

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    Overhead of
 every
 native call

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    JavaScript time

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    time JavaScript

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    Overhead of
 every
 native call Batch
 native calls

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    Shared
 mutable
 data

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    Native Objects JavaScript
 Objects

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    Shared
 mutable
 data Exchange
 serializable
 messages

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    Asynchronous Batched Serializable

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    The Bridge

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    Native Bridge JavaScript

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    Native Bridge JavaScript Event
 (touch, timer, networks, etc.) 1 Collect

    data and notify JS 2 Serialized payload 3 Process event 4 Call 0 – ∞ native methods 5 Update UI
 (if needed) 8 Serialized response 6 Process commands 7
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    JS is event-driven

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    Events Commands

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    Example

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    • Updates counter • Sends data to web service

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       render()  {          return  (  

               <View  style={styles.container}>                  <Text  style={styles.value}>                      {this.state.count}                  </Text>                  <Button                      title="Add  +1"                      onPress={()  =>  this.inc()}                  />              </View>          );      }
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       inc()  {          var  newCount  =

     this.state.count  +  1;          this.setState({count:  newCount});          fetch(              'https://api.conunter.io/',              {                  method:  'post',                  body:  'value='  +  newCount              }          );      }
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    Native UITouch [_bridge enqueueJSCall:@"EventEmitter.receiveTouches" args:@[@"end", @{@"x": @42, @"y": @106}]]; x,

    y, view, ...
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    Native Bridge JavaScript [ 'EventEmitter', 'receiveTouches', ['end', {'x': 42, 'y':

    106}] ] [_bridge enqueueJSCall:@"RCTEventEmitter.receiveTouches" args:@[@"end", @{@"x": @42, @"y": @106}]]; call('EventEmitter',  'receiveTouches',  [{x:  42,  y:  ...}])
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    function  call(moduleName,  methodName,  args)  {      MessageQueue.init();    

           var  module  =  require(moduleName);      module[methodName].apply(module,  args);            return  MessageQueue.flush();   } //  EventEmitter //  receiveTouches Message
 queue
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    Touch processing

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    What element
 should respond
 to a given event?

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    Button Button pressed!

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    Button Cancelled

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    Button Cancelled Scrollview

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    Button Scrolling stops Scrollview

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    Button Scrollview Horizontal Scrollview Navigator

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    Responder System

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    onStartShouldSetResponder onResponderTerminationRequest onResponderGrant onResponderMove onResponderRelease onResponderTerminate …

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    <TouchableOpacity>
 <TouchableHighlight>
 <TouchableBounce>
 <TouchableWithoutFeedback> onPress

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       inc()  {          var  newCount  =

     this.state.count  +  1;          this.setState({count:  newCount});          fetch(              'https://api.conunter.io/',              {                  method:  'post',                  body:  'value='  +  newCount              }          );      }
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             <View  style={...}>        

             <Text  style={...}>                      42                  </Text>                  <Button                      title="Add  +1"                      onPress={...}                  />              </View>          <View  style={...}>                  <Text  style={...}>                      43                  </Text>                  <Button                      title="Add  +1"                      onPress={...}                  />              </View> 42 43
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    var  UIManager  =  require('NativeModules').UIManager;   UIManager.update(18,  {text:  '43'}); Somewhere in

    React's internals:
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    NativeModules

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    NativeModules.UIManager  =  {      ...      update:  function(viewID,

     attributes)  {          MessageQueue.push(              ['UIManager',  'update',  [viewID,  attributes]]          );      }      ...   }; Message
 queue UIManager
 update  ..
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       inc()  {          var  newCount  =

     this.state.count  +  1;          this.setState({count:  newCount});          fetch(              'https://api.conunter.io/',              {                  method:  'post',                  body:  'value='  +  newCount              }          );      } Message
 queue UIManager
 update  .. DataManager
 query    ....
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    function  call(moduleName,  methodName,  args)  {      MessageQueue.init();    

           var  module  =  require(moduleName);      module[methodName].apply(module,  args);            return  MessageQueue.flush();   } Message
 queue UIManager
 update  .. DataManager
 query    ....
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    Native Bridge JavaScript [UIManager updateView:18 props:@{@"text": @"43"}] [DataManager query:@"post" url:@"http://..."]

    [ ['UIManager', 'update', [18, {text: '43'}]], ['DataManager', 'query', ['post', 'http://...']] ] Message
 queue UIManager
 update  .. DataManager
 query    ....
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    Native [UIManager updateView:18 props:@{@"text": @"43"}] addUIBlock:^() { UILabel *label =

    viewRegistry[18]; label.text = @"43"; [label markAsDirty]; }
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    Layout Layout github.com/facebook/css-layout

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    { margin: 20, borderBottomWidth: 2, flex: 1, alignContent: 'center', }

    { left: 120, top: 220, width: 60, height: 60, } Flexbox Coordinates
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    • User taps the button • Counter is updated

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    Native Bridge JavaScript Event
 (touch, timer, networks, etc.) 1 Collect

    data and notify JS 2 Serialized payload 3 Process event 4 Call 0 – ∞ native methods 5 Serialized response 6 Process commands 7 Update UI
 (if needed) 8
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    Benefits

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    Fast

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    Native Bridge JavaScript Event
 (touch, timer, networks, etc.) 1 Update

    UI
 (if needed) 8 Collect data and notify JS 2 Serialized payload 3 Process event 4 Call 0 – ∞ native methods 5 Serialized response 6 Process commands 7
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    Record / Replay

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    Flexible JS runtime

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    Native Bridge JavaScript

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    Native Bridge JavaScript Awesome App

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    Native Bridge JavaScript Awesome App WebKit process IPC

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    Native Bridge JavaScript Awesome App Chrome Debugger WebSockets

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    Live demo iPhone -> Chrome

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    None
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    None
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    Heroku iPhone

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    Streaming

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    None
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    UI = ƒ(data)

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    Thank you! github.com/frantic/tlv-2015 @alex_frantic