如何基于JavaScript判断图片是否加载完成

<div v-if="!it.sealTag"><br>　　<img :src="it.style"><br></div><br><div v-if="it.sealTag && it.isSys" style="margin-:70px;">
  <p >图片丢失，请点击<span @click="resetSign()">重新生成</span></p>
</div>js

this.list = res.data;
this.list.forEach((it) => {
  it.style = catUrl()+'seal/pic/' + it.sealPath;
  //判断sealpath能不能使用
  let ImgObj = new Image(); //判断图片是否存在 
  ImgObj.src = catUrl()+'seal/pic/' + it.sealPath;
  setTimeout(()=>{
    if (ImgObj.fileSize > 0 || (ImgObj.width > 0 && ImgObj.height > 0)) {
      //falsesealpath不可用，truesealPath可用
      this.$set(it,'sealTag',true);
     } else { 
      this.sealId = it.id;
      this.$set(it,'sealTag',false);
   }
},300)});

this.list = res.data;
this.list.forEach((it) => {
//判断sealpath能不能使用
let ImgObj = new Image(); 
//判断图片是否存在 
ImgObj.onload = () => {
  if (ImgObj.fileSize > 0 || (ImgObj.width > 0 && ImgObj.height > 0)) { // 判断图片的sealpath能不能正常显示图片
  // sealTag:false 不显示 重新生成 的提示
  this.$set(it,'sealTag',false);
  }
}
// sealTag:true 要显示 重新生成 的提示
 ImgObj.onerror = () => {
  this.sealId = it.id;
  this.$set(it,'sealTag',true);
 }
  it.style = catUrl()+'seal/pic/' + it.sealPath;
  ImgObj.src = catUrl()+'seal/pic/' + it.sealPath;
});