What JavaScript Developers Actually Build
JavaScript is everywhere. Before you write a job description, understand where your JS developer will work:
Frontend Web Development
The most common use case. JS developers using React, Vue, or Angular build:
- Interactive UIs - Forms, modals, dropdowns, data tables
- Single-Page Applications - Gmail, Notion, Figma-style apps that don't reload
- Dynamic content - Real-time updates, infinite scroll, search-as-you-type
Companies: Airbnb (React), Alibaba (Vue), Google (Angular)
Backend/Server Development
With Node.js, JavaScript runs on servers:
- REST APIs - CRUD operations, authentication, data processing
- Real-time services - Chat applications, live notifications (Slack, Discord)
- Microservices - Netflix uses Node.js for their API layer
Companies: Netflix, PayPal, LinkedIn, Uber
Full-Stack Development
Many JS developers work across both:
- Next.js/Nuxt - Server-rendered React/Vue apps
- MERN/MEAN stack - MongoDB, Express, React/Angular, Node.js
- Serverless - AWS Lambda, Vercel functions
Mobile Development
React Native lets JS developers build native iOS/Android apps:
- Companies using React Native: Instagram, Shopify, Discord, Coinbase
The Modern JavaScript Developer (2024-2026)
JavaScript has evolved significantly. Here's what separates modern JS developers:
ES6+ Is Non-Negotiable
If a candidate's code looks like this:
var self = this;
function callback(err, data) { ... }
They're writing 2014-era JavaScript. Modern JS looks like:
const data = await fetchData();
const filtered = items.filter(item => item.active);
Async Programming Mastery
The biggest skill differentiator. JavaScript is asynchronous by nature:
- Junior: Can use
async/awaitbut doesn't understand what's happening - Mid: Handles Promises, parallel requests, error boundaries
- Senior: Understands event loop, manages race conditions, optimizes performance
TypeScript Adoption
TypeScript (JavaScript with types) is now standard:
- Required at: Stripe, Airbnb, Slack, Microsoft
- Optional but preferred at: Most startups founded after 2020
- Strong JS developers learn TypeScript in 2-3 weeks
Skills Assessment by Business Need
If You're Building a Web Application
- Priority skills: DOM manipulation, event handling, state management
- Interview signal: "How would you build an autocomplete search?"
- Red flag: Can't explain event bubbling or debouncing
If You're Building APIs/Backend
- Priority skills: Async patterns, error handling, database integration
- Interview signal: "How do you handle 1000 concurrent requests?"
- Red flag: No understanding of the event loop
If You're Building Full-Stack
- Priority skills: Both frontend and backend patterns, build tools
- Interview signal: "Walk me through a request from browser to database and back"
- Red flag: Only knows one side deeply
Common Hiring Mistakes
1. Framework Obsession
"Must know React AND Vue AND Angular" is a red flag that you don't know your own stack. A strong JS developer learns any framework in 2-3 weeks. Test for JavaScript fundamentals.
2. Outdated Interview Questions
Don't ask about var vs let or prototype inheritance trivia. Ask about real problems: "This code is slow. How would you profile and fix it?"
3. Ignoring Fundamentals
JavaScript frameworks change yearly. JavaScript fundamentals don't. A developer who deeply understands closures, the event loop, and async patterns will outperform a "React expert" who can't debug without Stack Overflow.
4. Years-Based Requirements
"5+ years JavaScript experience" is meaningless. Someone with 2 years of modern JS (ES6+, TypeScript, modern tooling) often outperforms someone with 8 years who learned in the jQuery era and hasn't kept up.
Recruiter's Cheat Sheet
Questions That Reveal Skill Level
| Question | Junior Answer | Senior Answer |
|---|---|---|
| "Explain closures" | "It's when a function remembers variables" | Uses practical example: "I used closures to create private state in a module..." |
| "What happens when you click a button?" | "The click handler runs" | Explains event loop, bubbling, and potential performance implications |
| "How do you handle errors?" | "try/catch" | Discusses error boundaries, graceful degradation, logging strategies |
Resume Green Flags
- Specific metrics ("Reduced bundle size by 40%")
- Modern stack mentions (TypeScript, Vite, modern framework versions)
- Performance or accessibility improvements
- Open source contributions
Resume Red Flags
- Lists every framework ever (jQuery AND React AND Vue AND Angular)
- "Expert in JavaScript" but no specifics
- Only tutorial projects (TodoMVC, weather apps)
- No mention of testing
The JavaScript Ecosystem in 2026
Understanding the modern JavaScript landscape helps you evaluate candidates and set realistic expectations.
Build Tools and Bundlers
Modern JavaScript development requires understanding of build tools. Vite has largely replaced Webpack for new projects, offering faster development builds and simpler configuration. Candidates should understand why bundlers exist (code splitting, tree shaking, transpilation) even if they don't configure them daily.
Package Management
npm and pnpm are the dominant package managers. Experienced developers understand dependency management, lock files, and security implications of third-party packages. They know to audit dependencies and keep them updated.
Runtime Environments
JavaScript runs in browsers and on servers (Node.js, Deno, Bun). Each has different APIs and capabilities. A strong JavaScript developer understands these differences and can work effectively in their target environment.