What makes online compilers support many languages?

Question

Many online compilers can play with more various language than offline compilers.
Also, they provide compilers that treatment language that requires search hard to learn.
How can we play with so many languages on the online compilers?

Answer 1

because they provide a uniform frontend to many different compilers, they are not actually compilers themself, they might use gcc for c, g++ for c++, rustc for rust,...