I tried to remove one of the files in FileList, but I found that FileList is not an Array, and I cannot remove one of its elements through splice:
file: {
    files: FileList,
  }={
    files: {} as FileList
  }
 this.file.files.splice(index, 1);
// error message:
// Property 'splice' does not exist on type 'FileList'.
But through the for loop, you can see each file correctly:
for (let i = 0; i < this.file.files.length; i++) {
      let file = this.file.files[i]; 
      console.log(file);
    }
