Most agent bugs are really JavaScript bugs.
An agent juggles model calls that stream for a minute, tools that run in parallel and time out, users who press Stop halfway through, and conversations that outgrow memory and the model's context window. Frameworks hide those problems until they break in production. This book teaches you the language rules underneath, then shows you how to build the agent yourself.
Advanced JavaScript for the Agent Era goes from the inside out. Each chapter starts with a failure its own code reproduces, explains the mechanism behind it, and shows where that mechanism appears in nanoagent, a complete agent runtime with no dependencies that you build across the whole book.
What you will learn
- How JavaScript really works: scope, closures,
this, prototypes and classes, types, equality, and coercion. - Asynchronous JavaScript: the event loop, promises from the ground up, combinators,
async/await patterns, generators and async generators, streams and fetch, and cancellation with AbortSignal. - Functional and metaprogramming techniques: higher-order functions, iterators and iterator helpers,
Proxy, Reflect, symbols, and the observer pattern. - Modern JavaScript, ES2020 to ES2027: safer data handling, upgraded collections, binary data, resource management with
using, and Temporal. - Architecture, memory, and performance: modules, garbage collection, workers, and shared memory.
- Building AI agents with native JavaScript: the model loop, validated tools and schemas, streaming and stop controls, memory and context, multi-agent orchestration, and production guardrails, tracing, and tests.
How the book works
- 29 chapters in six parts, plus six appendices, including 100 interview questions, an event-loop cheat sheet, and a guide to running against a real model.
- The code runs on Node 24 or later. The examples were tested on Node 25.9 and 26.7.
- No API key needed: the agent examples run against a scripted model, so results are the same on every machine.
- No
npm install anywhere in the main text. - Every chapter opens with what you will learn, and ends with a summary and exercises with solutions.
Who it is for
Developers with one to three years of JavaScript who know the syntax, arrays and objects, fetch, and async/await, and who want to understand why their code behaves the way it does and build agents they can trust without a framework they cannot see inside.
