DOM real ou real
DOM
significa Document Object Model
(Document Object Model). Em termos simples, o DOM é a representação da interface do usuário (IU) em um aplicativo. Sempre que a IU muda, o DOM também é atualizado para refletir essas mudanças. A manipulação frequente de DOM tem um impacto negativo no desempenho.
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% !
