JS如何監聽div的resize事件詳解

阿新 • • 發佈：2020-12-06

需求

開發過程中經常遇到的一個問題就是如何監聽一個div的size變化。
比如我用canvas繪製了一個chart，當canvas的size發生變化的時候，需要重新繪製裡面的內容，這個時候就需要監聽resize事件做處理。

window上雖然可以新增resize事件監聽，但這並不能滿足我們的需求，因為很多時候，div的size發生了變化，但是window的size並沒有改變。

不過我們可以間接利用window的resize事件監聽來實現對於某個div的resize事件監聽，請看下面具體實現。

對於div的resize事件的監聽，實現方式有很多，比如週期性檢查，通過scroll事件等等，本文主要介紹通過object元素來實現監聽。

具體實現

/**
 * Created by taozh on 2017/5/6.
 * [email protected]
 */
var EleResize = {
 _handleResize: function (e) {
  var ele = e.target || e.srcElement;
  var trigger = ele.__resizeTrigger__;
  if (trigger) {
   var handlers = trigger.__z_resizeListeners;
   if (handlers) {
    var size = handlers.length;
    for (var i = 0; i < size; i++) {
     var h = handlers[i];
     var handler = h.handler;
     var context = h.context;
     handler.apply(context,[e]);
    }
   }
  }
 },_removeHandler: function (ele,handler,context) {
  var handlers = ele.__z_resizeListeners;
  if (handlers) {
   var size = handlers.length;
   for (var i = 0; i < size; i++) {
    var h = handlers[i];
    if (h.handler === handler && h.context === context) {
     handlers.splice(i,1);
     return;
    }
   }
  }
 },_createResizeTrigger: function (ele) {
  var obj = document.createElement('object');
  obj.setAttribute('style','display: block; position: absolute; top: 0; left: 0; height: 100%; width: 100%; overflow: hidden;opacity: 0; pointer-events: none; z-index: -1;');
  obj.onload = EleResize._handleObjectLoad;
  obj.type = 'text/html';
  ele.appendChild(obj);
  obj.data = 'about:blank';
  return obj;
 },_handleObjectLoad: function (evt) {
  this.contentDocument.defaultView.__resizeTrigger__ = this.__resizeElement__;
  this.contentDocument.defaultView.addEventListener('resize',EleResize._handleResize);
 }
};
if (document.attachEvent) {//ie9-10
 EleResize.on = function (ele,context) {
  var handlers = ele.__z_resizeListeners;
  if (!handlers) {
   handlers = [];
   ele.__z_resizeListeners = handlers;
   ele.__resizeTrigger__ = ele;
   ele.attachEvent('onresize',EleResize._handleResize);
  }
  handlers.push({
   handler: handler,context: context
  });
 };
 EleResize.off = function (ele,context) {
  var handlers = ele.__z_resizeListeners;
  if (handlers) {
   EleResize._removeHandler(ele,context);
   if (handlers.length === 0) {
    ele.detachEvent('onresize',EleResize._handleResize);
    delete ele.__z_resizeListeners;
   }
  }
 }
} else {
 EleResize.on = function (ele,context) {
  var handlers = ele.__z_resizeListeners;
  if (!handlers) {
   handlers = [];
   ele.__z_resizeListeners = handlers;

   if (getComputedStyle(ele,null).position === 'static') {
    ele.style.position = 'relative';
   }
   var obj = EleResize._createResizeTrigger(ele);
   ele.__resizeTrigger__ = obj;
   obj.__resizeElement__ = ele;
  }
  handlers.push({
   handler: handler,context);
   if (handlers.length === 0) {
    var trigger = ele.__resizeTrigger__;
    if (trigger) {
     trigger.contentDocument.defaultView.removeEventListener('resize',EleResize._handleResize);
     ele.removeChild(trigger);
     delete ele.__resizeTrigger__;
    }
    delete ele.__z_resizeListeners;
   }
  }
 }
}

測試程式碼：

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>Resize</title>
 <script src="./EleResize.js"></script>
 <style>
  html,body {
   margin: 0;
   padding: 0;
   width: 100%;
   height: 100%;
  }

  #resizeDiv {
   width: 60%;
   height: 60%;
   border: 1px solid red;
   margin: 20px;
  }

  button {
   margin: 20px 20px 0;
  }
 </style>
</head>
<body>
<button onclick="addListener()">addListener</button>
<button onclick="removeListener()">removeListener</button>
<button onclick="resize()">resize</button>
<div id="resizeDiv"></div>
<script>
 var resizeDiv = document.getElementById('resizeDiv');
 function resize() {
  resizeDiv.style.width = "200px";
 }
 var listener = function () {
  console.log("resize");
 };
 function addListener() {
  EleResize.on(resizeDiv,listener);
 }
 function removeListener() {
  EleResize.off(resizeDiv,listener)
 }
</script>
</body>
</html>