<el-upload
 class="upload-image"
 ref="upload"
 multiple
 :action="baseUrl"
 list-type="picture"
 :auto-upload="false"
 accept="image/*">
 <el-button slot="trigger" size="small" type="primary">选取文件</el-button>
 <el-button size="small" type="success" @click="submitUpload">上传到服务器</el-button>
 <div slot="tip">只能上传jpg、png、gif 格式，大小不超过500KB的图片</div>
</el-upload>

  submitUpload () {
   let { uploadFiles } = this.$refs.upload
   let form = new FormData()
   let status = true
   // 在这里对每一张图片进行大小的校验，如果不符合则提示，所有不符合的都提示，校验完成后只要有不符合条件的就不执行下面的操作
   uploadFiles.forEach(item => {
    const size = item.raw.size / 1024 <= 500
    if (!size) {
     this.$message.error(`${item.raw.name}大小超过500KB`)
     status = false
     return
    }
    form.append('image[]', item.raw)
   })
   if (!status) {
    return
   }
   // 符合条件后再将这个FormData对象传递给后端
   //调取接口上传form参数
   
 }

<el-upload
 class="upload-image"
 ref="upload"
 multiple
 :action="baseUrl"
 list-type="picture"
 :auto-upload="false"
 :before-upload="beforeImageUpload"
 :http-request="ImageRequest"
 accept="image/*">
 <el-button slot="trigger" size="small" type="primary">选取文件</el-button>
 <el-button size="small" type="success" @click="submitUpload">上传到服务器</el-button>
 <div slot="tip">只能上传jpg、png、gif 格式，大小不超过500KB的图片</div>
</el-upload>

beforeImageUpload (file) { // 上传文件前的钩子对文件进行校验
  const size = file.size / 1024 < 500
  if (!size) {
   this.$message.error('上传图片大小不能超过 500KB!')
  }
  return size
}

ImageRequest (file) {
  this.formData.append('image[]', file.file)
}

submitUpload () {
  this.formData = new FormData()
  // 手动触发上传
  this.$refs.upload.submit()
  // 此时所有的钩子已经执行完了formData 中存的是通过校验的数据
  // 此时在调用接口上传该数据
}