上传文件转base64

function getBase64(file) {
	return new Promise((resolve, reject) => {
		const reader = new FileReader();
		let fileResult = "";
		reader.readAsDataURL(file);
		// 开始转
		reader.onload = () => {
			fileResult = reader.result;
		};
		// 转 失败
		reader.onerror = error => {
			reject(error);
		};
		// 转 结束
		reader.onloadend = () => {
			resolve(fileResult);
		};
	});
}