Emil Hesslow
Software Engineer at Meta
Menlo Park, California, United States
Summary
👤
Senior🎓
Top SchoolEmil Hesslow is a software engineer with 19 years of experience based in Menlo Park, currently working on core Hack/PHP infrastructure at Meta where he focuses on usability improvements and server-side optimizations. He has deep expertise across backend systems, languages (Hack, PHP, Python, Java), search (Lucene), databases (MySQL), and browser extension development, and brings practical performance-first engineering to large-scale services. Emil is an active open-source contributor—his work on Facebook's HHVM includes refining blob encoding and performance cleanups, and he has improved UglifyJS with new compression strategies and unit testing. His career spans high-impact roles at Meta, Spotify, and other companies, reflecting both startup and large-platform experience. Colleagues rely on him for pragmatic, low-level improvements that yield measurable server savings and cleaner, more maintainable code.
19 years of coding experience
10 years of employment as a software developer
Computer Science, Computer Science at KTH Royal Institute of Technology
Github Skills (20)
unit-testing10
code-optimization10
algorithms10
javascript10
c-language10
uglifyjs10
php10
bytecode10
cprogramming-language10
optimization10
data-structure9
algorithm9
data-structures9
performance-tuning8
version-control8
Programming languages (10)
Github contributions (5)
facebook/hhvm
Aug 2013 - Jul 2021
A virtual machine for executing programs written in Hack.
Role in this project:
Back-end Developer
Back-end DeveloperContributions:258 commits, 27 comments in 8 years
Contributions summary:Emil's commits primarily focused on improving the codebase for the HHVM virtual machine, specifically related to the handling and encoding of data structures. The contributions involved refining the blob encoding for IndexedStringMap, including the removal of unnecessary code and improvements to the encoding process. They also made changes to the code to handle and encode information to be added for the repo, to load the functions from the repo. The commits also included a variety of performance optimizations and cleanup across the codebase.
hacklangphpvirtual-machineprogramshhvm
mishoo/UglifyJS-old
Oct 2010 - Feb 2011
JavaScript parser / mangler / compressor / beautifier library for NodeJS
Role in this project:Full-stack Developer
Full-stack DeveloperContributions:12 commits in 3 months
Contributions summary:Emil primarily contributed to the optimization and improvement of the JavaScript parser/mangler/compressor/beautifier library. Their work included implementing new compression techniques for string concatenation and assignment operations. The user also added a unit testing framework to verify fixes for issues. They demonstrated a strong focus on code quality and efficiency by refactoring and adding tests.
beautifierjavascriptcompressormanglernodejs
Find and Hire Top DevelopersWe’ve analyzed the programming source code of over 60 million software developers on GitHub and scored them by 50,000 skills. Sign-up on Prog,AI to search for software developers.