js <input type="file"> 设置

<input id="fileinput" type="file">
<script>
  // 通过拖拽事件document.addEventListener("drop",(event)=>{})的event.dataTransfer.items[0].getAsFile(),取得文件对象，再调用设置
  function setFileInputValue(file){
      const inputFile = document.getElementById('fileinput');
      const dataTransfer = new DataTransfer();
      dataTransfer.items.add(file);
      inputFile.files = dataTransfer.files;
      //手动触发change事件
      inputFile.dispatchEvent(new Event('change'));
  }

  function clearFileInput（）{
    const inputFile = document.getElementById('fileinput');
    inputFile.value="";
  }
</script>

参考：https://stackoverflow.com/questions/47119426/how-to-set-file-objects-and-length-property-at-filelist-object-where-the-files-a/47172409#47172409