react 源码解析 19. 手写迷你版 react
作者：zz1998
- 2021 年 12 月 08 日
本文字数：5420 字
阅读完需：约 18 分钟
react 源码解析 19.手写迷你版 react
视频讲解（高效学习）：进入学习
往期文章：
迷你 react 和真正的源码有哪些区别呢
在 render 阶段我们遍历了整颗 Fiber 树，在源码中如果节点什么都没改变会命中优化的逻辑，然后跳过这个节点的遍历
commit 我们也遍历了整颗 Fiber 树，源码中只遍历带有 effect 的 Fiber 节点，也就是遍历 effectList
每次遍历的时候我们都是新建节点，源码中某些条件会复用节点
没有用到优先级
第一步：渲染器和入口函数
const React = { createElement, render,};
const container = document.getElementById("root");
const updateValue = (e) => { rerender(e.target.value);};
const rerender = (value) => { const element = ( <div> <input onInput={updateValue} value={value} /> <h2>Hello {value}</h2> </div> ); React.render(element, container);};
rerender("World");
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第二步：创建 dom 节点函数
/创建elementfunction createElement(type, props, ...children) { return { type, props: { ...props, children: children.map((child) => (typeof child === "object" ? child : createTextElement(child))), }, };}
//创建text类型function createTextElement(text) { return { type: "TEXT_ELEMENT", props: { nodeValue: text, children: [], }, };}
//创建domfunction createDom(fiber) { const dom = fiber.type === "TEXT_ELEMENT" ? document.createTextNode("") : document.createElement(fiber.type);
updateDom(dom, {}, fiber.props);
return dom;}
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第三步：更新节点函数
const isEvent = (key) => key.startsWith("on");const isProperty = (key) => key !== "children" && !isEvent(key);const isNew = (prev, next) => (key) => prev[key] !== next[key];const isGone = (prev, next) => (key) => !(key in next);
//更新节点属性function updateDom(dom, prevProps, nextProps) { //删除老的事件 Object.keys(prevProps) .filter(isEvent) .filter((key) => !(key in nextProps) || isNew(prevProps, nextProps)(key)) .forEach((name) => { const eventType = name.toLowerCase().substring(2); dom.removeEventListener(eventType, prevProps[name]); });
// 删除旧属性 Object.keys(prevProps) .filter(isProperty) .filter(isGone(prevProps, nextProps)) .forEach((name) => { dom[name] = ""; });
// 设置新属性 Object.keys(nextProps) .filter(isProperty) .filter(isNew(prevProps, nextProps)) .forEach((name) => { dom[name] = nextProps[name]; });
// 增加新事件 Object.keys(nextProps) .filter(isEvent) .filter(isNew(prevProps, nextProps)) .forEach((name) => { const eventType = name.toLowerCase().substring(2); dom.addEventListener(eventType, nextProps[name]); });}
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第四步：render 阶段
//render阶段function performUnitOfWork(fiber) { if (!fiber.dom) { fiber.dom = createDom(fiber); }
const elements = fiber.props.children; reconcileChildren(fiber, elements);
if (fiber.child) { return fiber.child; } let nextFiber = fiber; while (nextFiber) { if (nextFiber.sibling) { return nextFiber.sibling; } nextFiber = nextFiber.parent; }}
//调协节点function reconcileChildren(wipFiber, elements) { let index = 0; let oldFiber = wipFiber.alternate && wipFiber.alternate.child; let prevSibling = null; while (index < elements.length || (oldFiber !== null && oldFiber !== undefined)) { const element = elements[index]; let newFiber = null;
const sameType = oldFiber && element && element.type === oldFiber.type;
if (sameType) { newFiber = { type: oldFiber.type, props: element.props, dom: oldFiber.dom, parent: wipFiber, alternate: oldFiber, effectTag: "UPDATE", }; } if (element && !sameType) { newFiber = { type: element.type, props: element.props, dom: null, parent: wipFiber, alternate: null, effectTag: "PLACEMENT", }; } if (oldFiber && !sameType) { oldFiber.effectTag = "DELETION"; deletions.push(oldFiber); }
if (oldFiber) { oldFiber = oldFiber.sibling; }
if (index === 0) { wipFiber.child = newFiber; } else if (element) { prevSibling.sibling = newFiber; } prevSibling = newFiber; index++; }}
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第五步：commit 阶段
//commit阶段function commitRoot() { deletions.forEach(commitWork); commitWork(wipRoot.child); currentRoot = wipRoot; wipRoot = null;}
//操作真实domfunction commitWork(fiber) { if (!fiber) { return; }
const domParent = fiber.parent.dom; if (fiber.effectTag === "PLACEMENT" && fiber.dom !== null) { domParent.appendChild(fiber.dom); } else if (fiber.effectTag === "UPDATE" && fiber.dom !== null) { updateDom(fiber.dom, fiber.alternate.props, fiber.props); } else if (fiber.effectTag === "DELETION") { domParent.removeChild(fiber.dom); }
commitWork(fiber.child); commitWork(fiber.sibling);}
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第六步：开始调度
//渲染开始的入口function render(element, container) { wipRoot = { dom: container, props: { children: [element], }, alternate: currentRoot, }; deletions = []; nextUnitOfWork = wipRoot;}
//调度函数function workLoop(deadline) { let shouldYield = false; while (nextUnitOfWork && !shouldYield) { //render阶段 nextUnitOfWork = performUnitOfWork(nextUnitOfWork); shouldYield = deadline.timeRemaining() < 1; }
if (!nextUnitOfWork && wipRoot) { commitRoot(); //commit阶段 }
requestIdleCallback(workLoop); //空闲调度}
requestIdleCallback(workLoop);
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完整代码
//创建elementfunction createElement(type, props, ...children) { return { type, props: { ...props, children: children.map((child) => (typeof child === "object" ? child : createTextElement(child))), }, };}
//创建text类型function createTextElement(text) { return { type: "TEXT_ELEMENT", props: { nodeValue: text, children: [], }, };}
//创建domfunction createDom(fiber) { const dom = fiber.type === "TEXT_ELEMENT" ? document.createTextNode("") : document.createElement(fiber.type);
updateDom(dom, {}, fiber.props);
return dom;}
const isEvent = (key) => key.startsWith("on");const isProperty = (key) => key !== "children" && !isEvent(key);const isNew = (prev, next) => (key) => prev[key] !== next[key];const isGone = (prev, next) => (key) => !(key in next);
//更新节点属性function updateDom(dom, prevProps, nextProps) { //删除老的事件 Object.keys(prevProps) .filter(isEvent) .filter((key) => !(key in nextProps) || isNew(prevProps, nextProps)(key)) .forEach((name) => { const eventType = name.toLowerCase().substring(2); dom.removeEventListener(eventType, prevProps[name]); });
// 删除旧属性 Object.keys(prevProps) .filter(isProperty) .filter(isGone(prevProps, nextProps)) .forEach((name) => { dom[name] = ""; });
// 设置新属性 Object.keys(nextProps) .filter(isProperty) .filter(isNew(prevProps, nextProps)) .forEach((name) => { dom[name] = nextProps[name]; });
// 增加新事件 Object.keys(nextProps) .filter(isEvent) .filter(isNew(prevProps, nextProps)) .forEach((name) => { const eventType = name.toLowerCase().substring(2); dom.addEventListener(eventType, nextProps[name]); });}
//commit阶段function commitRoot() { deletions.forEach(commitWork); commitWork(wipRoot.child); currentRoot = wipRoot; wipRoot = null;}
//操作真实domfunction commitWork(fiber) { if (!fiber) { return; }
const domParent = fiber.parent.dom; if (fiber.effectTag === "PLACEMENT" && fiber.dom !== null) { domParent.appendChild(fiber.dom); } else if (fiber.effectTag === "UPDATE" && fiber.dom !== null) { updateDom(fiber.dom, fiber.alternate.props, fiber.props); } else if (fiber.effectTag === "DELETION") { domParent.removeChild(fiber.dom); }
commitWork(fiber.child); commitWork(fiber.sibling);}
let nextUnitOfWork = null;let currentRoot = null;let wipRoot = null;let deletions = null;
//渲染开始的入口function render(element, container) { wipRoot = { dom: container, props: { children: [element], }, alternate: currentRoot, }; deletions = []; nextUnitOfWork = wipRoot;}
//调度函数function workLoop(deadline) { let shouldYield = false; while (nextUnitOfWork && !shouldYield) { //render阶段 nextUnitOfWork = performUnitOfWork(nextUnitOfWork); shouldYield = deadline.timeRemaining() < 1; }
if (!nextUnitOfWork && wipRoot) { commitRoot(); //commit阶段 }
requestIdleCallback(workLoop); //空闲调度}
requestIdleCallback(workLoop);
//render阶段function performUnitOfWork(fiber) { if (!fiber.dom) { fiber.dom = createDom(fiber); }
const elements = fiber.props.children; reconcileChildren(fiber, elements);
if (fiber.child) { return fiber.child; } let nextFiber = fiber; while (nextFiber) { if (nextFiber.sibling) { return nextFiber.sibling; } nextFiber = nextFiber.parent; }}
//调协节点function reconcileChildren(wipFiber, elements) { let index = 0; let oldFiber = wipFiber.alternate && wipFiber.alternate.child; let prevSibling = null; while (index < elements.length || (oldFiber !== null && oldFiber !== undefined)) { const element = elements[index]; let newFiber = null;
const sameType = oldFiber && element && element.type === oldFiber.type;
if (sameType) { newFiber = { type: oldFiber.type, props: element.props, dom: oldFiber.dom, parent: wipFiber, alternate: oldFiber, effectTag: "UPDATE", }; } if (element && !sameType) { newFiber = { type: element.type, props: element.props, dom: null, parent: wipFiber, alternate: null, effectTag: "PLACEMENT", }; } if (oldFiber && !sameType) { oldFiber.effectTag = "DELETION"; deletions.push(oldFiber); }
if (oldFiber) { oldFiber = oldFiber.sibling; }
if (index === 0) { wipFiber.child = newFiber; } else if (element) { prevSibling.sibling = newFiber; } prevSibling = newFiber; index++; }}
const React = { createElement, render,};
const container = document.getElementById("root");
const updateValue = (e) => { rerender(e.target.value);};
const rerender = (value) => { const element = ( <div> <input onInput={updateValue} value={value} /> <h2>Hello {value}</h2> </div> ); React.render(element, container);};
rerender("World");
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