Practical Abstract Syntax Trees

In this course, you'll learn the fundamentals of abstract syntax trees, what they are, how they work, and dive into several practical use cases of abstract syntax trees to maintain a JavaScript codebase.


What You Will Learn

Abstract syntax tree fundamentals

JavaScript tools that work with abstract syntax trees

How to parse, traverse, and generate abstract syntax trees

Practical skill set for maintaining large JavaScript codebases

In this course, we'll start with the fundamentals of abstract syntax trees (ASTs) and learn the basic mental models. This general AST knowledge can be translated to almost any tool that works with ASTs.

Why this course?

Understanding and using ASTs unlocks the ability to make sweeping changes in a safe and reliable way in any size codebase.

Course topics

Throughout this course, we'll have converted source code into ASTs, traversed, mutated, and generated ASTs. With these concepts we'll then explore several practical applications including things like code audits (static analysis), code transformations (codemods), and linting.

Module 1

We'll learn the fundamentals of abstract syntax trees.

  • What is an AST?
  • How to explore an AST
  • Examples of JavaScript tools that work with ASTs

Module 2

We'll learn how to work with ASTs.

  • How to turn code into an AST
  • How to programmatically navigate any AST
  • How to leverage TypeScript to prevent runtime errors

Module 3

We'll learn how to statically analyze, or "audit" code to understand the state of the codebase using abstract syntax trees.

  • An introduction to an example codebase and refactor
  • Understanding the state of the current codebase
  • When to use an AST-based tool versus doing something manually

Module 4

We'll learn how to transform, or "codemod" code from one state to another using abstract syntax trees.

  • How to make changes to an AST
  • How to change ASTs with jscodeshift
  • How to test a code transform

Module 5

We'll learn how to write rules, or "lint" code using abstract syntax trees.

  • How to create rules for code
  • How to create custom rules with ESLint
  • How to test a rule

Course Content

5 modules18 lessons1h 57m total


1 lesson 2m total

Course overview

Course overview


2:27 minutes

Understanding Abstract Syntax Trees (AST)

4 lessons 13m total

What is an AST?

Understand the basics of an AST and how it relates to real-world code


5:55 minutes

Exploring an AST

Looking at an example code snippet and how it relates to the resulting AST


4:21 minutes

JavaScript AST ecosystem

An overview of the tooling available in the web frontend (JavaScript) ecosystem that rely on ASTs


1:46 minutes

Environment setup

A quick overview of the basic environment setup used throughout this course


1:03 minutes

Working with Abstract Syntax Trees

3 lessons 23m total

Generating a JavaScript AST

Exploring tools to convert (or parse) JavaScript into a real AST


6:29 minutes

Traversing an AST

Programmatically traverse an AST and visit arbitrary nodes


7:33 minutes

Preventing Runtime Errors (with Types)

See how types can surface runtime errors


9:31 minutes

Code Audits

4 lessons 22m total

Practical code audits

A practical example of needing to perform a code audit (static analysis) to understand the current state of a codebase


2:35 minutes

Performing a code audit

Create a custom script to audit a codebase


15:29 minutes

Adding the Button component

Introduce a shared Button component to replace all existing button elements


2:32 minutes

When to use AST-based tooling

A rough formula to determine when to use AST-based tooling


1:43 minutes


3 lessons 37m total

Mutating an AST

Transforming code in place by mutating an AST


21:13 minutes

Using jscodeshift

Using jscodeshift to make the same code transformations with less boilerplate


10:03 minutes

Testing a transform

Create tests for jscodeshift transforms for a faster feedback loop


5:55 minutes


3 lessons 18m total

Creating rules for code

Implement a linting rule to prevent the code we just transformed from being reintroduced in the future


8:44 minutes

Using ESLint

Use ESLint to create the same linting rule for the code with less boilerplate


5:31 minutes

Testing custom linting rules

Testing custom ESLint linting rules to verify they work as expected


4:31 minutes

Your Instructors

Profile image for skovy

Spencer Miskoviak

👋 Hi! I'm Spencer, the author of this course. When I first heard about abstract syntax trees I thought they were something reserved for academia. After being faced with many large refactorings and seeking a way to automate it, I stumbled across ASTs. I was surprised by the versatility, practical uses, and everyday tooling that relies on ASTs. I shared one of these practical uses at React Conf in 2019 to remove 4MB of JavaScript.

This course distills the time I spent struggling through documentation in a way I wish I could have learned about abstract syntax trees and their applications in the frontend web ecosystem.

Frequently Asked Questions

Who is this course for?

This course is for anybody looking to understand the fundamentals of abstract syntax trees and how to apply them in a practical way to maintain and refactor a JavaScript/TypeScript codebase "at scale."

What if I need help?

You can ask us questions anytime through the community Discord channel or by sending us a message.

  • 18 lessons (1h 57m)

  • 1 complete project

  • 2,400 lines of code