Valid Base64 String Regex
Regex to test for a valid base64 string. Encoding at the start of the string must
be removed (e.g. data:image/gif;base64,R0lGOD...==)
1const base64Regex = /^([0-9a-zA-Z+/]{4})*(([0-9a-zA-Z+/]{2}==)|([0-9a-zA-Z+/]{3}=))?$/2