index.js

function resizeListener(e) {
  var win = e.target || e.srcElement
  if (win.__resizeRAF__) {
    cancelAnimationFrame(win.__resizeRAF__)
  }
  win.__resizeRAF__ = requestAnimationFrame(function () {
    var trigger = win.__resizeTrigger__
    var listeners = trigger && trigger.__resizeListeners__
    if (listeners) {
      listeners.forEach(function (fn) {
        fn.call(trigger, e)
      })
    }
  })
}

var _exports = function exports(element, fn) {
  var window = this
  var document = window.document
  var isIE

  var attachEvent = document.attachEvent
  if (typeof navigator !== "undefined") {
    isIE =
      navigator.userAgent.match(/Trident/) || navigator.userAgent.match(/Edge/)
  }

  function objectLoad() {
    this.contentDocument.defaultView.__resizeTrigger__ = this.__resizeElement__
    this.contentDocument.defaultView.addEventListener("resize", resizeListener)
  }

  if (!element.__resizeListeners__) {
    element.__resizeListeners__ = []
    if (attachEvent) {
      element.__resizeTrigger__ = element
      element.attachEvent("onresize", resizeListener)
    } else {
      if (getComputedStyle(element).position === "static") {
        element.style.position = "relative"
      }
      var obj = (element.__resizeTrigger__ = document.createElement("object"))
      obj.setAttribute(
        "style",
        "position: absolute; top: 0; left: 0; height: 100%; width: 100%; pointer-events: none; z-index: -1; opacity: 0;"
      )
      obj.setAttribute("class", "resize-sensor")

      // prevent <object> from stealing keyboard focus
      obj.setAttribute("tabindex", "-1")

      // prevent screenreaders to see this object
      obj.setAttribute("title", "")

      obj.__resizeElement__ = element
      obj.onload = objectLoad
      obj.type = "text/html"
      if (isIE) {
        element.appendChild(obj)
      }
      obj.data = "about:blank"
      if (!isIE) {
        element.appendChild(obj)
      }
    }
  }
  element.__resizeListeners__.push(fn)
}

module.exports =
  typeof window === "undefined" ? _exports : _exports.bind(window)

module.exports.unbind = function (element, fn) {
  var attachEvent = document.attachEvent
  var listeners = element.__resizeListeners__ || []
  if (fn) {
    var index = listeners.indexOf(fn)
    if (index !== -1) {
      listeners.splice(index, 1)
    }
  } else {
    listeners = element.__resizeListeners__ = []
  }
  if (!listeners.length) {
    if (attachEvent) {
      element.detachEvent("onresize", resizeListener)
    } else if (element.__resizeTrigger__) {
      var contentDocument = element.__resizeTrigger__.contentDocument
      var defaultView = contentDocument && contentDocument.defaultView
      if (defaultView) {
        defaultView.removeEventListener("resize", resizeListener)
        delete defaultView.__resizeTrigger__
      }
      element.__resizeTrigger__ = !element.removeChild(
        element.__resizeTrigger__
      )
    }
    delete element.__resizeListeners__
  }
}