DataScript is a Minecraft mod that allows writing lua code like regular mcfunctions. Because complex calculations and string manipulation operations are not easily possible with Minecraft commands, lua code can be used to perform such operations. DataScript provides object-oriented wrappers for game apis which normally would be accessible through minecraft commands.
WARNING: DataScript is NOT a sandbox for lua code. Like every ordinary java mod, the lua code from the world's datapacks can include any code, malicious code too. That is why a downloaded world has to be inspected by the server operator or singleplayer user BEFORE joining or playing.