Make side-effect.js smaller (#6118)

Start at making side-effect.js / head.js smaller.

Author: timneutkens

packages/next-server/lib/head-manager-context.ts

@@ -1,3 +1,3 @@
 import * as React from 'react'
 
-export const HeadManagerContext = React.createContext(null)
+export const HeadManagerContext: React.Context<any> = React.createContext(null)

packages/next-server/lib/head.js

@@ -1,16 +1,7 @@
 import React from 'react'
-import PropTypes from 'prop-types'
-import sideEffect from './side-effect'
+import withSideEffect from './side-effect'
 import { HeadManagerContext } from './head-manager-context'
 
-class Head extends React.Component {
-  static contextType = HeadManagerContext
-
-  render () {
-    return null
-  }
-}
-
 const NEXT_HEAD_IDENTIFIER = 'next-head'
 
 export function defaultHead (className = NEXT_HEAD_IDENTIFIER) {
@@ -41,22 +32,12 @@ function reduceComponents (components) {
     })
 }
 
-function mapOnServer (head) {
-  return head
-}
-
-function onStateChange (head) {
-  if (this.context) {
-    this.context.updateHead(head)
-  }
-}
-
 const METATYPES = ['name', 'httpEquiv', 'charSet', 'itemProp']
 
 /*
  returns a function for filtering head child elements
- which shouldn't be duplicated, like <title/>,
- except we explicit allow it in ALLOWED_DUPLICATES array
+ which shouldn't be duplicated, like <title/>
+ Also adds support for deduplicated `key` properties
 */
 
 function unique () {
@@ -99,12 +80,14 @@ function unique () {
   }
 }
 
-if (process.env.NODE_ENV === 'development') {
-  const exact = require('prop-types-exact')
+const Effect = withSideEffect()
 
-  Head.propTypes = exact({
-    children: PropTypes.node.isRequired
-  })
+function Head ({children}) {
+  return <HeadManagerContext.Consumer>
+    {(updateHead) => <Effect reduceComponentsToState={reduceComponents} handleStateChange={updateHead}>{children}</Effect>}
+  </HeadManagerContext.Consumer>
 }
 
-export default sideEffect(reduceComponents, onStateChange, mapOnServer)(Head)
+Head.rewind = Effect.rewind
+
+export default Head

packages/next-server/lib/side-effect.js

@@ -0,0 +1,57 @@
+import React, { Component } from 'react'
+
+const isServer = typeof window === 'undefined'
+
+type State = React.DetailedReactHTMLElement<any, any>[] | undefined
+
+type SideEffectProps = {
+  reduceComponentsToState: (components: React.ReactElement<any>[]) => State,
+  handleStateChange?: (state: State) => void
+}
+
+export default function withSideEffect () {
+  const mountedInstances: Set<any> = new Set()
+  let state: State
+
+  function emitChange (component: React.Component<SideEffectProps>) {
+    state = component.props.reduceComponentsToState([...mountedInstances])
+    if(component.props.handleStateChange) {
+      component.props.handleStateChange(state)
+    }
+  }
+
+  class SideEffect extends Component<SideEffectProps> {
+    // Used when server rendering
+    static rewind () {
+      const recordedState = state
+      state = undefined
+      mountedInstances.clear()
+      return recordedState
+    }
+
+    constructor (props: any) {
+      super(props)
+      if (isServer) {
+        mountedInstances.add(this)
+        emitChange(this)
+      }
+    }
+    componentDidMount () {
+      mountedInstances.add(this)
+      emitChange(this)
+    }
+    componentDidUpdate () {
+      emitChange(this)
+    }
+    componentWillUnmount () {
+      mountedInstances.delete(this)
+      emitChange(this)
+    }
+
+    render () {
+      return null
+    }
+  }
+
+  return SideEffect
+}

packages/next-server/lib/side-effect.tsx

@@ -10,7 +10,7 @@ export default class HeadManager {
     this.updatePromise = null
   }
 
-  updateHead (head) {
+  updateHead = (head) => {
     const promise = this.updatePromise = Promise.resolve().then(() => {
       if (promise !== this.updatePromise) return
 

packages/next/client/head-manager.js

@@ -181,7 +181,7 @@ async function doRender ({ App, Component, props, err, emitter: emitterProp = em
   // In development runtime errors are caught by react-error-overlay.
   if (process.env.NODE_ENV === 'development') {
     renderReactElement((
-      <HeadManagerContext.Provider value={headManager}>
+      <HeadManagerContext.Provider value={headManager.updateHead}>
         <App {...appProps} />
       </HeadManagerContext.Provider>
     ), appContainer)
@@ -196,7 +196,7 @@ async function doRender ({ App, Component, props, err, emitter: emitterProp = em
     }
     renderReactElement((
       <ErrorBoundary onError={onError}>
-        <HeadManagerContext.Provider value={headManager}>
+        <HeadManagerContext.Provider value={headManager.updateHead}>
           <App {...appProps} />
         </HeadManagerContext.Provider>
       </ErrorBoundary>