根据URL实现转Blob

export function dataURItoBlob(base64Data) {
	var byteString;
	byteString = window.atob(base64Data.split(',')[1]);
	var mimeString = base64Data.split(',')[0].split(':')[1].split(';')[0];
	var ab = new ArrayBuffer(byteString.length)
	var ia = new Uint8Array(byteString.length);
	for (var i = 0; i < byteString.length; i++) {
		ia[i] = byteString.charCodeAt(i);
	}
	return new Blob([ia], {
		type: mimeString
	});
}