base64转file对象

/**
 * base64 转 File 对象
 * @param url base64
 * @param fileName 文件名
 */
const base64ToFile = (url: string, fileName?: string) => {
    let arr = url.split(','),
    mime = arr[0].match(/:(.*?);/)![1],
    bstr = atob(arr[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n);

    while (n--) {
    	u8arr[n] = bstr.charCodeAt(n);
    }

    return new File([u8arr], fileName!, { type: mime });
};