Comment by Sarath C on "What programming languages are used at Facebook?"

Facebook is a major contributor to Open Source Software. They open source nearly all useful technologies that go in their product across platforms like iOS, Android, Web, Backend and hardware technologies.

Going by the GitHub Page of Facebook, they heavily uses C++, Java, JavaScript, Python and Objective-C.

Presto written in Java
RocksDB, a persistent key value storage, written in C++
Facebook Historically written in PHP and solid contributor to its community. HHVM is a high performance JIT appoach . This is primarily written in C++ and PHP
We talk more about Facebook when it comes to JavaScript stack. React is their most popula open source project.
Looks like they're yet to catch hold of Swift.

You can see more here - code.facebook.com/projects

Someone from Facebook can contribute better to the answer.

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