element-ui Upload 通过Js来触发上传操作

最简单的文件上传如下：

<el-upload
  class="upload-demo"
  action="https://jsonplaceholder.typicode.com/posts/"
  >
  <el-button size="small" type="primary">上传</el-button>
</el-upload>

现在有一个需求是点击“上传”不直接打开文件选择框，而是通过条件判断来决定是否打开文件选择框

<div>
    <el-upload
      ref="uploadRef"
      class="upload-demo"
      action="https://jsonplaceholder.typicode.com/posts/"
     />
     <el-button size="small" type="primary" @click="handleUpload">点击上传</el-button>
 </div>
 // js方法
 methods: {
  handleUpload(){
    let flag = ture
    if(flag) {
      this.$refs.uploadRef.submit()
    } else {
      alert('无法选择文件')
    }
  }
}