三
三月小生

把学习和生活慢慢写下来

技术

runtime-core 实现

# 前端 # Vue

第一步

packages/runtime-core/package.json

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{
  "name": "@vue/runtime-core",
  "version": "1.0.0",
  "module": "dist/runtime-core.esm-bundler.js",
  "unpkg": "dist/runtime-core.global.js",
  "buildOptions": {
    "name": "RuntimeCore",
    "formats": [
      "esm-bundler",
      "esm-browser",
      "cjs",
      "global"
    ]
  },
  "dependencies": {
    "@vue/reactivity": "workspace:^1.0.0",
    "@vue/shared": "workspace:^1.0.0"
  }
}

由于 runtime-dom 依赖了 runtime-core，因此需要在 runtime-dom 中安装一下，pnpm i @vue/runtime-core@workspace --filter @vue/runtime-dom

runtime-core 依赖了 reactivity，因此执行 pnpm i @vue/reactivity@workspace @vue/shared@workspace --filter @vue/runtime-core

第二步

实现 createRenderer 函数

packages/runtime-core/src/index.ts

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export * from './renderer';

packages/runtime-core/src/renderer.ts

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import { ShapeFlags } from '@vue/shared';
import { Fragment, isSameVnode, Text } from './createVnode';
import getSequence from './seq';

export function createRenderer(renderOptions) {
  const {
    insert: hostInsert,
    remove: hostRemove,
    createElement: hostCreateElement,
    createText: hostCreateText,
    setText: hostSetText,
    setElementText: hostSetElementText,
    parentNode: hostParentNode,
    nextSibling: hostNextSibling,
    patchProp: hostPatchProp,
  } = renderOptions;

  const mountChildren = (children, container) => {
    for (let i = 0; i < children.length; i++) {
      patch(null, children[i], container);
    }
  };

  const mountElement = (vnode, container, anchor) => {
    const { type, children, props, shapeFlag } = vnode;
    const el = vnode.el = hostCreateElement(type);
    if (props) {
      for (const key in props) {
        hostPatchProp(el, key, null, props[key]);
      }
    }

    if (shapeFlag & ShapeFlags.TEXT_CHILDREN) {
      hostSetElementText(el, children);
    } else if (shapeFlag & ShapeFlags.ARRAY_CHILDREN) {
      mountChildren(children, el);
    }

    hostInsert(el, container, anchor);
  };

  const processElement = (n1, n2, container, anchor) => {
    if (n1 === null) {
      mountElement(n2, container, anchor);
    } else {
      patchElement(n1, n2, container);
    }
  };

  const processText = (n1, n2, container) => {
    if (n1 === null) {
      hostInsert(n2.el = hostCreateText(n2.children), container);
    } else {
      const el = n2.el = n1.el;
      if (n1.children !== n2.children) {
        hostSetText(el, n2.children);
      }
    }
  };

  const processFragment = (n1, n2, container) => {
    if (n1 === null) {
      mountChildren(n2.children, container);
    } else {
      patchChildren(n1, n2, container);
    }
  };

  const patchProps = (oldProps, newProps, el) => {
    for (const key in newProps) {
      hostPatchProp(el, key, oldProps[key], newProps[key]);
    }

    for (const key in oldProps) {
      if (!(key in newProps)) {
        hostPatchProp(el, key, oldProps[key], null);
      }
    }
  };

  const unmountChildren = (children) => {
    for (let i = 0; i < children.length; i++) {
      const child = children[i];
      unmount(child);
    }
  };

  const patchKeyChildren = (c1, c2, el) => {
    let i = 0;
    let e1 = c1.length - 1;
    let e2 = c2.length - 1;

    // 从头开始比较
    while (i <= e1 && i <= e2) {
      const n1 = c1[i];
      const n2 = c2[i];

      if (isSameVnode(n1, n2)) {
        patch(n1, n2, el);
      } else {
        break;
      }
      i++;
    }

    // 从尾部比较
    while (i <= e1 && i <= e2) {
      const n1 = c1[e1];
      const n2 = c2[e2];
      if (isSameVnode(n1, n2)) {
        patch(n1, n2, el);
      } else {
        break;
      }
      e1--;
      e2--;
    }

    if (i > e1) {
      // 新的多
      if (i <= e2) {
        // 查看当前元素的下一个元素是否存在
        const nextPos = e2 + 1;
        const anchor = c2[nextPos]?.el;
        while (i <= e2) {
          patch(null, c2[i], el, anchor);
          i++;
        }
      }
    } else if (i > e2) {
      // 老的多
      if (i <= e1) {
        while (i <= e1) {
          // 删除老的
          unmount(c1[i]);
          i++;
        }
      }
    } else {
      // 上面两个判断，是确认没有变化的节点，同时处理了插入和删除
      // 上面比完了开头和结尾，下面是比较中间部分
      // 比较中间部分的时候，是拿新的去老的里面找，如果找到的话，就用老的，没有找到的话，就新建
      let s1 = i;
      let s2 = i;

      // 创建一个映射表，保存新的，用于查找老的在新的里面是否还有，如果有的话，就更新，没有的话，就删除
      const keyToNewIndexMap = new Map();
      // 要插入的个数
      const toBePatched = e2 - s2 + 1;
      let newIndexToOldMapIndex = new Array(toBePatched).fill(0);

      for (let j = s2; j <= e2; j++) {
        const vnode = c2[j];
        keyToNewIndexMap.set(vnode.key, j);
      }

      for (let j = s1; j <= e1; j++) {
        const vnode = c1[j];
        const newIndex = keyToNewIndexMap.get(vnode.key);
        if (newIndex === undefined) {
          // 在新的里面找不到老的
          unmount(vnode);
        } else {
          // 比较前后节点的差异，更新属性和儿子
          newIndexToOldMapIndex[newIndex - s2] = j + 1;
          patch(vnode, c2[newIndex], el);
        }
      }

      const increasingSeq = getSequence(newIndexToOldMapIndex);

      let j = increasingSeq.length - 1;

      // 调整顺序，按照新的，使用 insertBefore 倒序插入
      for (let i = toBePatched - 1; i >= 0; i--) {
        const newIndex = s2 + i;
        const anchor = c2[newIndex + 1]?.el;

        const vnode = c2[newIndex];

        // 如果是需要新建的，那么 el 这个属性的值是空的
        if (!vnode.el) {
          patch(null, vnode, el, anchor);
        } else {
          if (i === increasingSeq[j]) {
            j--;
          } else {
            hostInsert(vnode.el, el, anchor);
          }
        }

      }
    }
  };

  const patchChildren = (n1, n2, el) => {
    const c1 = n1.children;
    const c2 = n2.children;

    const preShapeFlag = n1.shapeFlag;
    const shapeFlag = n2.shapeFlag;

    if (shapeFlag & ShapeFlags.TEXT_CHILDREN) {
      // 新的是文本，老的是数组，移除老的
      if (preShapeFlag & ShapeFlags.ARRAY_CHILDREN) {
        unmountChildren(c1);
      }

      // 新的是文本，老的也是文本，替换内容
      if (c1 !== c2) {
        hostSetElementText(el, c2);
      }
    } else {
      if (preShapeFlag & ShapeFlags.ARRAY_CHILDREN) {
        if (shapeFlag & ShapeFlags.ARRAY_CHILDREN) {
          // 老的是数组，新的也是数组，那就全量 diff 算法，是两个数组的比对
          patchKeyChildren(c1, c2, el);
        } else {
          // 老的是数组，新的不是数组，移除老的
          unmountChildren(c1);
        }
      } else {
        // 老的是文本，新的是空
        if (preShapeFlag & ShapeFlags.TEXT_CHILDREN) {
          hostSetElementText(el, '');
        }

        // 老的是文本，新的是数组
        if (shapeFlag & ShapeFlags.ARRAY_CHILDREN) {
          mountChildren(c2, el);
        }
      }
    }
  };

  const patchElement = (n1, n2, container) => {
    const el = n2.el = n1.el;
    const oldProps = n1.props || {};
    const newProps = n2.props || {};
    patchProps(oldProps, newProps, el);
    patchChildren(n1, n2, el);
  };

  // 渲染和更新都走这里
  const patch = (n1, n2, container, anchor = null) => {
    if (n1 === n2) {
      return;
    }
    if (n1 && !isSameVnode(n1, n2)) {
      unmount(n1);
      n1 = null;
    }

    const { type } = n2;

    switch (type) {
      case Text:
        processText(n1, n2, container);
        break;
      case Fragment:
        processFragment(n1, n2, container);
        break;
      default:
        processElement(n1, n2, container, anchor);
    }
  };

  const unmount = (vnode) => {
    if (vnode.type === Fragment) {
      unmountChildren(vnode.children)
    } else {
      hostRemove(vnode.el);
    }
  }

  // 多次调用 render，会进行虚拟节点的比较，然后再进行更新
  const render = (vnode, container) => {
    if (vnode === null) {
      if (container._vnode) {
        unmount(container._vnode);
      }
    } else {
      patch(container._vnode || null, vnode, container);
      container._vnode = vnode;
    }
  };
  return {
    render
  };
}

packages/runtime-core/src/seq.ts

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export default function getSequence(arr) {
  const result = [ 0 ];
  const p = result.slice(0);
  let start;
  let end;
  let middle;
  const len = arr.length;
  for (let i = 0; i < len; i++) {
    const arrI = arr[i];
    if (arrI !== 0) {
      const resultLastIndex = result[result.length - 1];
      if (arr[resultLastIndex] < arrI) {
        p[i] = result[result.length - 1];
        result.push(i);
        continue;
      }
    }

    start = 0;
    end = result.length - 1;

    while (start < end) {
      middle = ((start + end) / 2) | 0;
      if (arr[result[middle]] < arrI) {
        start = middle + 1;
      } else {
        end = middle;
      }
    }

    if (arrI < arr[result[start]]) {
      p[i] = result[start - 1];
      result[start] = i;
    }
  }

  let l = result.length;
  let last = result[l - 1];

  while (l-- > 0) {
    result[l] = last;
    last = p[last];
  }

  return result;
}

packages/shared/src/shapeFlags.ts

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export enum ShapeFlags {
  ELEMENT = 1,
  FUNCTIONAL_COMPONENT = 1 << 1,
  STATEFUL_COMPONENT = 1 << 2,
  TEXT_CHILDREN = 1 << 3,
  ARRAY_CHILDREN = 1 << 4,
  SLOTS_CHILDREN = 1 << 5,
  TELEPORT = 1 << 6,
  SUSPENSE = 1 << 7,
  COMPONENT_SHOULD_KEEP_ALIVE = 1 << 8,
  COMPONENT_KEPT_ALIVE = 1 << 9,
  COMPONENT = ShapeFlags.STATEFUL_COMPONENT | ShapeFlags.FUNCTIONAL_COMPONENT,
}

packages/shared/src/index.ts

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export * from './shapeFlags';

...

在 patchKeyChildren 函数中实现的 diff 算法

  1. 在比较新的和老的时候，由于两个都是数组，所以比较的时候，先从头开始比较，当遇到不一样的节点的时候，就结束当前比较，再从尾部开始比较，然后确定范围
  2. 在比较的时候，如果有多余的或者新增的话，就直接操作即可，在比较的时候，是同层比较，一层一层的比较，递归进行的