React实现核心Diff算法的示例代码

// 更新前
<ul>
  <li key="0" className="before">0</li>
  <li key="1">1</li>
</ul>

// 更新后
<ul>
  <li key="0" className="after">0</li>
  <li key="1">1</li>
</ul>

// 更新前
<ul>
  <li key="0">0</li>
  <li key="1">1</li>
  <li key="2">2</li>
</ul>

// 更新后 情况1 —— 新增节点
<ul>
  <li key="0">0</li>
  <li key="1">1</li>
  <li key="2">2</li>
  <li key="3">3</li>
</ul>

// 更新后 情况2 —— 删除节点
<ul>
  <li key="0">0</li>
  <li key="1">1</li>
</ul>

// 更新前
<ul>
  <li key="0">0</li>
  <li key="1">1</li>
</ul>

// 更新后
<ul>
  <li key="1">1</li>
  <li key="0">0</li>
</ul>

type Flag = 'Placement' | 'Deletion';

interface node {
  key: string;
  flag?: Flag;
  index?: number;
}

type NodeList = Node[];

function diff(before: NodeList, after: NodeList): NodeList {
  // ...代码
}

// 更新前
const before = [
  {key: 'a'}
]
// 更新后
const after = [
  {key: 'd'}
]

// diff(before, after) 输出
[
  {key: "d", flag: "Placement"},
  {key: "a", flag: "Deletion"}
]

// 更新前
const before = [
  {key: 'a'},
  {key: 'b'},
  {key: 'c'},
]
// 更新后
const after = [
  {key: 'c'},
  {key: 'b'},
  {key: 'a'}
]

// diff(before, after) 输出
[
  {key: "b", flag: "Placement"},
  {key: "a", flag: "Placement"}
]

function diff(before: NodeList, after: NodeList): NodeList {
  const result: NodeList = [];

  // ...遍历前的准备工作

  for (let i = 0; i < after.length; i++) {
    // ...核心遍历逻辑
  }

  // ...遍历后的收尾工作

  return result;
}

// 保存结果
const result: NodeList = [];
  
// 将before保存在map中
const beforeMap = new Map<string, Node>();
before.forEach((node, i) => {
  node.index = i;
  beforeMap.set(node.key, node);
})

// 更新前
const before = [
  {key: 'a'},
  {key: 'b'}
]
// 更新后
const after = [
  {key: 'b'}
]

// 遍历到的最后一个可复用node在before中的index
let lastPlacedIndex = 0;  

// 遍历到的最后一个可复用node在before中的index
let lastPlacedIndex = 0;  

for (let i = 0; i < after.length; i++) {
const afterNode = after[i];
afterNode.index = i;
const beforeNode = beforeMap.get(afterNode.key);

if (beforeNode) {
  // 存在可复用node
  // 从map中剔除该 可复用node
  beforeMap.delete(beforeNode.key);

  const oldIndex = beforeNode.index as number;

  // 核心判断逻辑
  if (oldIndex < lastPlacedIndex) {
    // 移动
    afterNode.flag = 'Placement';
    result.push(afterNode);
    continue;
  } else {
    // 不移动
    lastPlacedIndex = oldIndex;
  }

} else {
  // 不存在可复用node，这是一个新节点
  afterNode.flag = 'Placement';
  result.push(afterNode);
}

// 更新前
const before = [
  {key: 'a'},
  {key: 'b'}
]
// 更新后
const after = [
  {key: 'b'}
]

beforeMap.forEach(node => {
  node.flag = 'Deletion';
  result.push(node);
});