React portal 主要用于解决组件树和 DOM 树的结构之间不一致的问题。portal 将 DOM 树上不同位置上的组件连接到一起,最为常使用的场景就是将 Modal 弹窗覆盖整个视窗。 // Assume an empty div with id 'modal' is in your HTML const modalEl = document.getElementById("modal"); function Modal({ child...
React.memo也是通过记忆组件渲染结果的方式来提高性能,memo是react16.6引入的新属性,通过浅比较(源码通过Object.is方法比较)当前依赖的props和下一个props是否相同来决定是否重新渲染;如果使用过类组件方式,就能知道memo其实就相当于class组件中的React.PureComponent,区别就在于memo用于函数组件,pureComponent用于类组件(pureCom...
window.requestIdleCallback = window.requestIdleCallback || function(handler) {let startTime = Date.now();return setTimeout(function() {handler({didTimeout: false,timeRemaining: function() {return Math.max(0, 50.0 - (Date.now() - startTime));}});}, 1);} 严格来说,这不能算是一个 ...
源码在packages/react-reconciler/src/ReactFiberHooks.js中可以找到: 代码语言:typescript AI代码解释 functionupdateMemo<T>(nextCreate:()=>T,deps:Array<mixed>|void|null,):T{consthook=updateWorkInProgressHook();constnextDeps=deps===undefined?null:deps;constprevState=hook.memoizedState;// Assume these...
functionApp() { const counteRef=useRef(); const handleClick= () => {counteRef.current.click();}//ref对象获取到子组件暴露出来的对象。return(<React.Fragment> <Counter ref={counteRef}></Counter> //ref对象赋值给子组件的ref属性。Add </React.Fragment>); } 如果项目中使用了...
import React, { memo, useCallback, useState } from 'react' const Logger = memo((props) => { props.log() return null }) export default function App() { const [count, setCount] = useState(0) const count5 = Math.floor(count / 5) ...
import React, { memo } from "react"; const ChildComponent = memo(function ChildComponent({ text }) { console.log("ChildComponent rendered"); return {text}; }); function ParentComponent({ showChild }) { return ( {showChild && <Child...
https://www.react.express/hooks/usecallback useCallback The useCallback hook lets us memoize functions. The return value will be the same function (comparable with ===) for the lifecycle of the component, unless the dependencies array changes. If the dependencies change, then a new function...
action inline ouruseMemohook was relying on an unstable function reference. Each time we changed the AmountField, we ended up creating a new debounced function and immediately firing off the call to update our rate table. To solve this problem we wrap our dispatched action function inuseCall...
实现React requestIdleCallback 调度能力 React内部实现了该方法 requestIdleCallback,即一帧空闲执行任务,但Schedular + Lane 模式远比 requestIdleCallback 复杂的多。这里我们先通过了解 requestIdleCallback都做了些什么,再尝试通过 requestAnimationFrame + MessageChannel 来模拟 React 对一帧空闲判断的实现。