Decoding JavaScript Code: The Reasons Behind Abstract Syntax Trees

Demystifying How JS Engines Understand Your Code

Photo by Ian Keefe on Unsplash

When you write code in a high-level programming language like JavaScript, you naturally think about the logic, variables, functions, and output you want. But under the hood, some fascinating and complex processes happen every time your JS code runs.

Your code first passes through a JavaScript parser whose job is to analyze and understand what you wrote. The output is an abstract syntax tree (AST) that represents the structure of your code in a format the JavaScript engine can understand. This intermediary step is crucial.

In this article, we’ll unpack why ASTs exist, how they reflect code structure, and what role they play in compiling and executing JavaScript.

Bringing Structure and Meaning to Code

At their core, ASTs exist because computer processors don’t understand human languages or free-flowing code with all its punctuation, white space, shorthand symbols and human-friendly syntax.

ASTs take your nicely formatted code and transform it into a structured tree-like format that highlights relationships and hierarchy for the compiler.