调用上传方法时报错 “ Uncaught (in promise): Error: _getFileSize requires Buffer/File/String.”

[jocklei]

作者，你好，在开发客户端的时候调用方法 'multipartUpload'时报错，报错信息如下：

ERROR Error: Uncaught (in promise): Error: _getFileSize requires Buffer/File/String.
Error: _getFileSize requires Buffer/File/String.

请问，怎么会事儿？如何解决？thank you！

附，其他信息：
1、使用的是angular4框架，组件化开发；
2、语言：typescript；
3、此组件所有代码如下：

`import { Component, OnInit, Input, Output, EventEmitter } from '@angular/core';

declare const OSS: any;

@component({
selector: 'app-file-upload-oss',
templateUrl: './file-upload-oss.component.html',
styleUrls: ['./file-upload-oss.component.scss']
})

export class FileUploadOssComponent implements OnInit {

// configuration parameter
@input() type?: String = 'rectangle';
@input() region: string;
@input() accessKeyId: string;
@input() accesskey: string;

@input()
set bucket(val: string) {
if (val !== '' && val.indexOf('/') !== val.length - 1) {
val = val + '/';
}
this._bucket = val;
};
get bucket(): string {
return this._bucket;
};

@output() uploadStatus = new EventEmitter();

_bucket: string;
filesList: any[] = [];

// Handle files
handleFiles(files: any[]) {
return new Promise((resolve) => {
for (const file of files) {
file['loading'] = false;
file['remove'] = false;
file['percent'] = 0;
};
resolve(files);
});
};

// click select files
clickSelectFiles($event: any) {
this.filesList.length = 0;

this.handleFiles($event.target.files).then((files: any[]) => {
  this.filesList.push(...files);
});

};

// dragover preventDefault
dragover($event: any) {
$event.preventDefault();
};

// drop select files
dropSelectFiles($event: any) {
$event.preventDefault();

this.handleFiles($event.dataTransfer.files).then((files: any[]) => {
  this.filesList.push(...files);
});

};

// remove files
removeFile(index: number) {
this.filesList[index]['removeAnimation'] = 'fadeOutRight';
setTimeout(() => {
this.filesList.splice(index, 1);
}, 300);
};

// upload files
uploadFile() {
const file = document.getElementById('btn')['files'][0];
const files = this.filesList;
const key = 'object';

const client = new OSS.Wrapper({
  region: this.region,
  accessKeyId: this.accessKeyId,
  accessKeySecret: this.accesskey,
  bucket: this.bucket
});

client.multipartUpload(key, file, {
  progress: this.progress
}).then(((res: any) => {
  alert(`${res}`);
  console.log('upload success');
  this.uploadStatus.emit(res);
}));

};

// upload progress
progress(p: any) {
console.log(进度${p});
};

constructor() { }

ngOnInit() {
}

}
`