mini-vue.html

<div id="app"></div>

<script>
  /* vdom开始 */
  function h(tag, props, children) {
    return {
      tag,
      props, 
      children
    }
  }

  function mount(vnode, container) {
    const el = vnode.el = document.createElement(vnode.tag)
    // props
    if(vnode.props) {
      for (const key in vnode.props) {
        const value = vnode.props[key]
        // 简化版事件处理
        if(key.startsWith("on")) {
          el.addEventListener(key.slice(2).toLowerCase(), value)
        } else {
          // 属性处理
          el.setAttribute(key, value)
        }
      }
    }
      

    // children
    if(vnode.children) {
      if (typeof vnode.children === "string") {
        el.textContent = vnode.children
      } else {
        vnode.children.forEach(child => {
          // if (typeof child === "string") {}
          mount(child, el)
        });
      }

    }

    container.appendChild(el)
  }

  function patch(n1, n2) {
    if (n1.tag === n2.tag) {
      const el = n2.el =  n1.el
      // props
      const oldProps = n1.props || {}
      const newProps = n2.props || {}
      for (const key in newProps) {
        const oldValue = oldProps[key]
        const newValue = newProps[key]
        if (newValue !== oldValue) {
          el.setAttribute(key, newValue)
        }
      }
      for (const key in oldProps) {
       if (!(key in newProps)) {
         el.removeAttribute(key)
       }
      }

      // children
      const oldChildren = n1.children
      const newChildren = n2.children
      if (typeof newChildren === "string") {
        if (typeof oldChildren === "string") {
          if (newChildren !== oldChildren) {
            el.textContent = newChildren
          }
        } else {
          el.textContent = newChildren
        }
      } else {
        if (typeof oldChildren === "string") {
          el.innerHTML = ""
          newChildren.forEach(child => {
            mount(child, el)
          })
        } else {
          const commonLength = Math.min(oldChildren.length, newChildren.length)
          for (let i = 0; i <commonLength; i++) {
            patch(oldChildren[i], newChildren[i])
          }
          if (newChildren.length > oldChildren.length) {
            newChildren.slice(oldChildren.length).forEach(child => {
              mount(child, el)
            })
          } else if (newChildren.length < oldChildren.length) {
            el.removeChild(child.el)
          }
        }
      }
    } else {
      //replace
    }
  }
  /* vdom结束 */

  /* reactivity开始 */
  let activeEffect

  class Dep {
    subscribers = new Set()

    depend() {
      if (activeEffect) {
        this.subscribers.add(activeEffect)
      }
    }

    notify() {
      this.subscribers.forEach(effect => {
        effect()
      })
    }
  }

  function watchEffect(effect) {
    activeEffect = effect
    effect()
    activeEffect = null
  }

  const targetMap = new WeakMap()

  function getDep(target, key) {
    let depsMap = targetMap.get(target)
    if (!depsMap) {
      depsMap = new Map()
      targetMap.set(target ,depsMap)
    }
    let dep  = depsMap.get(key)

    if(!dep) {
      dep = new Dep()
      depsMap.set(key, dep)
    }

    return dep
  }

  const reactiveHandlers = {
    get(target, key, receiver) {
      const dep = getDep(target, key)
      dep.depend()
      // return targetp[key]
      return Reflect.get(target, key, receiver)
    },
    set(target, key, value, receiver) {
      const dep = getDep(target, key)
      const result = Reflect.set(target, key, value, receiver)
      dep.notify()
      return result
    }
  }

  function reactive(raw) {
    return new Proxy(raw, reactiveHandlers)
  }
  /* reactivity结束 */

  const App = {
    data: reactive({
      count: 0
    }),
    render() {
      // 转String是因为patch并没有处理children为number的情况
      return h("div", {
        onClick: () => {
          this.data.count++
        }
      }, String(this.data.count))
    }
  }

  function mountApp(component, container) {
    let isMounted = false,
      prevVdom
    watchEffect(() => {
      if (!isMounted) {
        prevVdom = component.render()
        mount(prevVdom, container)
        isMounted = true
      } else {
        const newVdom = component.render()
        patch(prevVdom, newVdom)
        prevVdom = newVdom
      }
    })
  }

  mountApp(App, document.getElementById("app"))
</script>