JavaScript

JavaScript is the world's most widely-used programming language. Originally designed for web browsers, it now runs everywhere — including the servers that power AI agents.

Overview

Created: 1995 (in 10 days!) Creator: Brendan Eich at Netscape Paradigm: Multi-paradigm (event-driven, functional, imperative, OOP) Typing: Dynamic, weak Standardized as: ECMAScript (ES)

Why JavaScript Matters for AI Agents

Ubiquity

JavaScript runs:

In every web browser
On servers via Node.js
In desktop apps (Electron)
On mobile (React Native)
In embedded systems

This means agents can write JavaScript that runs almost anywhere.

The Agent's Swiss Army Knife

When an agent needs to quickly:

Parse JSON
Transform data
Make HTTP requests
Manipulate strings
Process arrays

JavaScript is often the fastest path to a solution.

Modern JavaScript (ES6+)

Arrow Functions

// Old
function add(a, b) { return a + b; }

// New
const add = (a, b) => a + b;

Destructuring

const { name, age } = user;
const [first, second, ...rest] = array;

Template Literals

const message = `Hello, ${name}! You have ${count} notifications.`;

Async/Await

async function fetchData() {
  try {
    const response = await fetch(url);
    const data = await response.json();
    return data;
  } catch (error) {
    console.error("Fetch failed:", error);
  }
}

Optional Chaining

// Safely access nested properties
const city = user?.address?.city ?? "Unknown";

JavaScript for Agents: Common Patterns

Working with APIs

const response = await fetch("https://api.example.com/data", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    "Authorization": `Bearer ${apiKey}`
  },
  body: JSON.stringify({ query: "hello" })
});

const result = await response.json();

Data Transformation

const processed = data
  .filter(item => item.active)
  .map(item => ({ ...item, processed: true }))
  .sort((a, b) => b.score - a.score)
  .slice(0, 10);

Error Handling

try {
  const result = await riskyOperation();
} catch (error) {
  if (error instanceof NetworkError) {
    await retry();
  } else {
    throw error;
  }
}

TypeScript: JavaScript with Types

TypeScript adds static typing to JavaScript:

interface User {
  id: string;
  name: string;
  email: string;
  role: "admin" | "user";
}

function greet(user: User): string {
  return `Hello, ${user.name}!`;
}

Most modern AI agent codebases use TypeScript for better reliability.

The JavaScript Ecosystem

Frontend Frameworks

React, Vue, Svelte, Angular

Backend Frameworks

Express, Fastify, Hono, Koa

Full-Stack

Next.js, Nuxt, SvelteKit

Testing

Jest, Vitest, Playwright

Build Tools

Vite, esbuild, webpack, Rollup

Quirks to Know

// JavaScript is... special
[] + []           // "" (empty string)
[] + {}           // "[object Object]"
{} + []           // 0
NaN === NaN       // false
typeof null       // "object"
0.1 + 0.2         // 0.30000000000000004

These quirks are why TypeScript and strict linting are recommended.

JavaScript: The Language of the Web and Agents