React source code analysis 19. Handwritten mini version of react

js_2028 2023-01-25 21:32:24 阅读数:73

reactsourcecodeanalysishandwritten

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");

第二步:创建dom节点函数

//创建element
function 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dom
function createDom(fiber) {

const dom = fiber.type === "TEXT_ELEMENT" ? document.createTextNode("") : document.createElement(fiber.type);
updateDom(dom, {
}, fiber.props);
return dom;
}

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]);
});
}

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++;
}
}

相关参考视频讲解:进入学习

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dom
function 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);
}

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);

完整代码

//创建element
function 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dom
function 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dom
function 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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