Element resize 监听

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resize-observer-polyfill

  1. 元素新增字段 __resizeListeners__ 存放 resize 事件回调
  2. 元素新增字段 __ro__ 存放新增 resize-observer 实例对象
  3. 使用resize-observer 实例对象 监听(调用 observe 实例方法)监听当前元素

ResizeObserver 类

  1. 实例化:new ResizeObserver(handler) 接收回调函数
  2. 实例方法:
    • ro.observe(Element) 监听节点resize
    • ro.disconnect() 取消节点监听事件
import ResizeObserver from 'resize-observer-polyfill'

const isServer = typeof window === 'undefined'

/* istanbul ignore next */
const resizeHandler = function (entries) {
  for (const entry of entries) {
    const listeners = entry.target.__resizeListeners__ || []
    if (listeners.length) {
      listeners.forEach(fn => {
        fn()
      })
    }
  }
}

/* istanbul ignore next */
export const addResizeListener = function (element, fn) {
  if (isServer) return
  if (!element.__resizeListeners__) {
    element.__resizeListeners__ = []
    element.__ro__ = new ResizeObserver(resizeHandler)
    element.__ro__.observe(element)
  }
  element.__resizeListeners__.push(fn)
}

/* istanbul ignore next */
export const removeResizeListener = function (element, fn) {
  if (!element || !element.__resizeListeners__) return
  element.__resizeListeners__.splice(element.__resizeListeners__.indexOf(fn), 1)
  if (!element.__resizeListeners__.length) {
    element.__ro__.disconnect()
  }
}