迷你 react

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

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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

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function createElement(type, props, ...children) {
  //创建element
  return {
    type,
    props: {
      ...props,
      children: children.map((child) =>
        typeof child === "object" ? child : createTextElement(child)
      ),
    },
  };
}

function createTextElement(text) {
  //创建text类型
  return {
    type: "TEXT_ELEMENT",
    props: {
      nodeValue: text,
      children: [],
    },
  };
}

function createDom(fiber) {
  //创建dom
  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

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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);
function updateDom(dom, prevProps, nextProps) {
  //更新节点属性

  //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

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function performUnitOfWork(fiber) {
  //render阶段
  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;
  }
}

function reconcileChildren(wipFiber, elements) {
  //reconcile节点
  let index = 0;
  let oldFiber = wipFiber.alternate && wipFiber.alternate.child;
  let prevSibling = null;

  while (index < elements.length || oldFiber != null) {
    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++;
  }
}

第五步：commit 阶段

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function commitRoot() {
  //commit阶段
  deletions.forEach(commitWork);
  commitWork(wipRoot.child);
  currentRoot = wipRoot;
  wipRoot = null;
}

function commitWork(fiber) {
  //操作真实dom
  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

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function render(element, container) {
  //渲染开始的入口
  wipRoot = {
    dom: container,
    props: {
      children: [element],
    },
    alternate: currentRoot,
  };
  deletions = [];
  nextUnitOfWork = wipRoot;
}

let nextUnitOfWork = null;
let currentRoot = null;
let wipRoot = null;
let deletions = null;

function workLoop(deadline) {
  //调度函数
  let shouldYield = false;
  while (nextUnitOfWork && !shouldYield) {
    nextUnitOfWork = performUnitOfWork(
      //render阶段
      nextUnitOfWork
    );
    shouldYield = deadline.timeRemaining() < 1;
  }

  if (!nextUnitOfWork && wipRoot) {
    commitRoot(); //commit阶段
  }

  requestIdleCallback(workLoop); //空闲调度
}

requestIdleCallback(workLoop);