JavaScript engine is the program that executes JavaScript code, whether that's in a browser or on a server. It reads the code, compiles it to machine code, and runs it - all so web developers can build fancy user interfaces without worrying about the nitty gritty details of registers and memory addresses.

How to use it in a sentence

Did you hear about the new JavaScript engine in Chrome? I heard it's so fast that it can execute an infinite loop in under 10 seconds!

I was trying to debug this memory leak in our Node.js app, but then I realized it was just the JavaScript engine doing garbage collection every 5 milliseconds - guess that's what happens when you try to run a blockchain on a potato.

If you actually want to learn more...

• JavaScript engine fundamentals: Shapes and Inline Caches: This article dives into some of the key optimizations that make modern JavaScript engines so dang fast, like using "shapes" to optimize property access. Warning: contains words like "polymorphism".

• JavaScript Engines: The Good Parts™: A talk that explains how JavaScript engines work under the hood, from the perspective of someone who actually works on them. Spoiler alert: it's a lot of graphs and weird acronyms.

• How JavaScript works: inside the V8 engine: An in-depth look at how Chrome's V8 engine optimizes JavaScript code, with tips on how to write code that doesn't make the engine sad. Apparently using eval() is like putting a "kick me" sign on your code's back.

Note: the Developer Dictionary is in Beta. Please direct feedback to skye@statsig.com.