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Stoyan Stefanov is a Facebook engineer, ex-Yahoo, architect of the YSlow 2.0 performance tool and creator of the image optimization tool.

He's the author of React: Up and Running (O'Reilly), JavaScript for PHP developers (O'Reilly), JavaScript Patterns (O'Reilly), Object-Oriented JavaScript (Packt Publishing), The Book of Speed (online), and a contributor to High-Performance JavaScript (O'Reilly) and Even Faster Web Sites (O'Reilly).

Stoyan blogs at and and has spoken at conferences and meetups around the world (Velocity, JSConf, OSCON, Web Directions, Fronteers...). He also runs the annual "Planet Performance Calendar" publication.

A Bulgarian-Canadian, Stoyan lives in Los Angeles with his wife and daughters and spends his offline hours biking around the beach and making music (rarely at the same time though).