React Native's inability to transfer binary data from and to native Android and iOS code means most bridged data is transferred in base64. Since React Native also doesn't include a buildin decode/encode we have to use a polyfill, which is painfully slow.
This 'polyfill' decodes base64 quickly into a Uint8Array in O(n). It manages to do so by skipping all default base64 validation checks, a mapped table, and directly converting to byte code.
Please note that this code does not validate your base64, it's meant to be a dumb and fast as possible implementation.