DOM réel ou réel
DOM
signifie Document Object Model
(Document Object Model). En termes simples, le DOM est la représentation de l'interface utilisateur (UI) dans une application. Chaque fois que l'interface utilisateur change, le DOM est également mis à jour pour refléter ces changements. Les manipulations fréquentes du DOM ont un impact négatif sur les performances.
DOM ?
DOM . DOM . ( ) () UI . — . , UI, DOM.
DOM . , JavaScript-. , JavaScript- DOM , .
, 10 . . . 10 , ! 1 , 9 .
— , - DOM. . React (virtual) DOM (VDOM).
DOM
React DOM ( — RDOM) VDOM. VDOM — RDOM, . VDOM , RDOM, , .
DOM (VDOM) — , «» UI «» DOM, , ReactDOM. (reconcilation).
RDOM . VDOM , () . VDOM ( ) .
VDOM ?
UI , VDOM . . , . (diffed) .
RDOM. , RDOM. , , RDOM.
DOM- .
, . UI, . DOM-. UI. , RDOM.
React VDOM?
, , VDOM, , React.
1. React «» (observer)
React UI (state). , React VDOM. VDOM, React . « » (diffing).
, VDOM, React RDOM. DOM. React JavaScript.
2. React (batch) RDOM
. (, ) .
UI — , React RDOM.
3. React
React O(n) () , :
key
()
.
, React . .
, React
DOM.
componentWillUnmount()
. , DOM DOM.UNSAFE_componentWillMount()
,componentDidMount()
. , ,
, , , . , :
<div> <Counter /> </div> <span> <Counter /> </span>
Counter
.
, React «» . DOM , . :
<div className="before" title="stuff" /> <div className="after" title="stuff" />
className
.
DOM, React .
React DOM- .
, , :
<ul>
<li></li>
<li></li>
</ul>
<ul>
<li></li>
<li></li>
<li></li>
</ul>
React "", <li></li>
<li></li>
, <li></li>
.
, . , :
<ul>
<li></li>
<li></li>
</ul>
<ul>
<li></li>
<li></li>
<li></li>
</ul>
React , <li></li>
<li></li>
.
React () key
. , React . , :
<ul>
<li key="1"></li>
<li key="2"></li>
</ul>
<ul>
<li key="0"></li>
<li key="1"></li>
<li key="2"></li>
</ul>
React , 0
, 1
2
.
, , :
<li key={item.id}>{item.name}</li>
, - . , .
, . , . .
. . , . , , , .
: « React, UI, DOM . , , , , , DOM».
React. , — , React. .
« DOM» — , , . React « DOM», , React-, , . , React , «» (fibers). . Fiber
— , React 16. VDOM.
VDOM?
« DOM» (). , VDOM — JavaScript-.
, DOM-:
:
const vdom = { tagName: 'html', children: [ { tagName: 'head' }, { tagName: 'body', children: [ { tagName: 'ul', attributes: { class: 'list' }, children: [ { tagName: 'li', attributes: { class: 'list_item' }, textContent: ' ', }, // li ], }, // ul ], }, // body ], } // html
VDOM. RDOM, HTML- (). , , , RDOM .
, . , list
, :
const list = { tagName: 'ul', attributes: { class: 'list' }, children: [ { tagName: 'li', attributes: { class: 'list_item' }, textContent: ' ', }, ], }
VDOM
, VDOM .
, VDOM , DOM. , DOM API.
, VDOM , . DOM API, .
const copy = { tagName: 'ul', attributes: { class: 'list' }, children: [ { tagName: 'li', attributes: { class: 'list_item' }, textContent: ' ', }, { tagName: 'li', attributes: { class: 'list_item' }, textContent: ' ', }, ], }
«» (diff) VDOM (list
) . Diff
:
const diffs = [ { newNode: { /* */ }, oldNode: { /* */ }, index: { /* */ }, }, { newNode: { /* */ }, index: { /* ... */ }, }, ]
diff
RDOM. DOM .
, , :
const domElement = document.quesrySelector('list') diffs.forEach((diff) => { const newElement = document.createElement(diff.newNode.tagName) /* ... */ if (diff.oldNode) { // , domElement.replaceChild(diff.newNode, diff.oldNode) } else { // , domElement.append(diff.newNode) } })
, , VDOM.
VDOM
, VDOM .
VDOM , React Vue DOM. , React list
:
import React from 'react' import ReactDOM from 'react-dom' const list = React.createElement( 'ul', { className: 'list' }, React.createElement('li', { className: 'list_item' }, ' ') ) // React «JSX» // const list = <ul className="list"><li className="list_item"> </li></ul> ReactDOM.render(list, document.body)
ReactDOM.render()
:
const newList = React.createElement( 'ul', { className: 'list' }, React.createElement( 'li', { className: 'list_item' }, ' ' ), React.createElement('li', { className: 'list_item' }, ' ') ) const timerId = setTimeout(() => { ReactDOM.render(newList, document.body) clearTimeout(timerId) }, 5000)
React VDOM, , , .
VDOM, , . DOM-, , DOM. , -.
, Angular
, , (single page applications, SPA) , Dirty Model Checking
( ). , DMC VDOM . MVC- . React , React — , , (view).
VDS .
10% !
