element-ui upload組件上傳圖片時限制圖片寬高

template部分代碼，引入upload組件，這里采用自動上傳文件

<div class="filesC">
       <el-upload
         ref="files"
         name="imgFile"
         class="avatar-uploader"
         :with-credentials="true"
         :action="action"
         :show-file-list="false"
         :on-success="handleAvatarSuccess"
         :on-error="handleAvatarError"
         :before-upload="beforeAvatarUpload">
         <img v-if="imageUrl" :src="imageUrl" class="avatar">
         <i v-else class="el-icon-plus avatar-uploader-icon"></i>
       </el-upload>
       &nbsp;圖片尺寸：141*54
</div>

script部分代碼，圖片上傳之前觸發 beforeAvatarUpload ，在這里return false 會中斷上傳操作

beforeAvatarUpload (file) {
  let _this = this
  if (file.type.indexOf('image')<0) {
    this.$alert({message: '圖片格式不正確', btn: false})
    return false
  }
  const isLt2M = file.size / 1024 / 1024 < 2;
  const isSize = new Promise(function(resolve, reject) {
    let width = 141;
    let height = 54;
    let _URL = window.URL || window.webkitURL;
    let img = new Image();
    img.onload = function() {
      let valid = img.width == width && img.height == height;
      valid ? resolve() : reject();
    }
    img.src = _URL.createObjectURL(file);
  }).then(() => {
    return file;
  }, () => {
    _this.$alert({message: '上傳的icon必須是等於141*54!', btn: false})
    return Promise.reject();
  });
  return isSize
},
handleAvatarSuccess (res, file) {
  if (res.state==200) {
    this.imageUrl = URL.createObjectURL(file.raw);//從文件中讀取的本地文件路徑，用於顯示在img標簽里
    this.fileUrl = res.data//上傳成功后，后台給返回的圖片線上路徑
  }else{
    this.$alert({message: '上傳失敗', btn: false})
  }

},
handleAvatarError (res, file) {
  this.$alert({message: '選擇圖片失敗', btn: false})
  /*this.imageUrl = URL.createObjectURL(file.raw);*/
},

css代碼，修改原組件的樣式

.filesC .avatar-uploader .el-upload {
  border: 1px solid #aaa;
  border-radius: 6px;
  cursor: pointer;
  position: relative;
  overflow: hidden;
}
.filesC .avatar-uploader .el-upload:hover {
  border-color: #409EFF;
}
.filesC .avatar-uploader-icon {
  font-size: 20px;
  color: #8c939d;
  width: 141px;
  height: 54px;
  line-height: 54px;
  text-align: center;
  background: white;
}
.filesC .avatar {
  width: 141px;
  height: 54px;
  display: block;
}