React.js Tutorial
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Tutorials React.js Tutorial

JSX If Statements — Complete Guide

JSX If Statements — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of React.js Tutorial on Toolliyo Academy.

8 min read Updated 6/23/2026
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React.js Tutorial · Lesson 9 of 100

ESLint & Prettier

Beginner → Intermediate → Advanced → Professional

Beginner · 1 — Foundations · ~12 min read · Module 1: Introduction & Setup

Introduction

This lesson is part of the beginner section. We explain ESLint & Prettier slowly, with examples you can copy and run. If something is unclear, read it twice — that is how everyone learns. ESLint finds code problems (unused variables, missing hook rules). Prettier formats code (indentation, quotes) so it looks consistent. Consistent style makes code reviews easier. ESLint catches React-specific mistakes like missing dependency arrays in useEffect.

ESLint & Prettier is setup knowledge. Without it, nothing else in React will run. Spend time here until commands work without copy-paste errors.

When will you use this?

You need this before writing any React code — same as installing Word before writing a document.

  • Every React job expects you to run projects locally with Node and a build tool like Vite.
  • Interviewers often ask you to clone a repo and run npm install && npm run dev on day one.

Real-world: catch hook bugs before merge

A Freshdesk engineer forgets userId in a useEffect dependency array — infinite refetch loop in staging. ESLint react-hooks plugin flags it in the PR before customers see a frozen inbox.

Production-style code

// .eslintrc.cjs
module.exports = {
  extends: ['eslint:recommended', 'plugin:react/recommended', 'plugin:react-hooks/recommended'],
  rules: {
    'react-hooks/rules-of-hooks': 'error',
    'react-hooks/exhaustive-deps': 'warn'
  }
};

// Flagged code in PR:
useEffect(() => {
  loadTickets(filter); // uses filter but deps missing
}, []); // ⚠ react-hooks/exhaustive-deps

What happens in production: Common React foot-guns are caught locally and in CI — same guardrails used at Meta, Airbnb, and Indian product companies.

Lesson example (start here)

Copy this smaller example first. Once it works, compare it with the real-world code above.

npm install -D eslint prettier eslint-config-prettier
// .eslintrc or eslint.config.js enables rules for React

Line-by-line walkthrough

CodeWhat it means
npm install -D eslint prettier eslint-config-prettierPart of the ESLint & Prettier example — read it together with the lines before and after.
// .eslintrc or eslint.config.js enables rules for ReactComment — notes for humans; the computer ignores it.

How it works (big picture)

  • ESLint warns in the editor.
  • Prettier runs on save to auto-format.
  • Together they reduce silly bugs and formatting debates.

Do this on your computer

  1. Add ESLint to a Vite project: npm create vite often includes a lint option.
  2. Install Prettier and enable format on save in VS Code.
  3. Fix red squiggles before committing code.
  4. Read the real-world section and name which part of the app uses this topic.
  5. Run the example locally and confirm the same behavior in the browser.
  6. Change one value in the example (text, initial state, or URL) and predict what will happen before you save.

Experiments — try changing this

  • Change text or labels in the example and save — watch the browser update.
  • Break the code on purpose (remove a bracket), read the error message, then fix it.

Remember

ESLint = catch bugs and bad patterns. Prettier = auto-format code. Fix lint errors early.

Common questions

Is linting required?

Not required to run React, but strongly recommended on real projects.

How long should I spend on ESLint & Prettier?

Until you can explain it in your own words and run the example without looking at the answer. Beginners often need 30–60 minutes per new hook or routing topic; setup lessons may take one afternoon.

What if I get stuck on ESLint & Prettier?

Re-read the line-by-line walkthrough, check the browser console for red errors, and compare your code character-by-character with the example. Search the exact error text — someone else had it too.

Where is ESLint & Prettier used in real jobs?

See the real-world section above — the same pattern appears in LMS, banking, e-commerce, and SaaS products. Interviewers ask you to explain it using one concrete example from your project or this lesson.

React.js Tutorial
Course syllabus
Module 1: React Basics & Setup Introduction to React — Complete Guide React Get Started — Complete Guide Your First React App — Complete Guide React Render HTML — Complete Guide ES6 for React — Complete Guide JSX Intro — Complete Guide JSX Expressions — Complete Guide JSX Attributes — Complete Guide JSX If Statements — Complete Guide React Components — Complete Guide
Module 2: Props, Events & Lists React Props — Complete Guide Props Destructuring — Complete Guide Props Children — Complete Guide React Events — Complete Guide React Conditionals — Complete Guide React Lists & Keys — Complete Guide React CSS Styling — Complete Guide Controlled Forms — Complete Guide Form Submit — Complete Guide Multiple Form Inputs — Complete Guide
Module 3: Forms & Hooks Textarea & Select — Complete Guide Checkbox & Radio — Complete Guide useState — Complete Guide useEffect — Complete Guide useRef — Complete Guide useContext — Complete Guide useReducer — Complete Guide useCallback — Complete Guide useMemo — Complete Guide Custom Hooks — Complete Guide
Module 4: Routing & Data React Router — Complete Guide Nested Routing — Complete Guide Protected Routes — Complete Guide Lazy Routes — Complete Guide React Portals — Complete Guide Fetch API — Complete Guide Axios — Complete Guide Error Handling — Complete Guide Context API — Complete Guide React Hook Form — Complete Guide
Module 5: State & Authentication Form Validation — Complete Guide Async Forms — Complete Guide Zustand — Complete Guide Redux Toolkit — Complete Guide TanStack Query — Complete Guide Optimistic Updates — Complete Guide Query Caching — Complete Guide Authentication Flows — Complete Guide React 19 Features — Complete Guide package.json & Tooling — Complete Guide
Module 6: Architecture & React 19 Enterprise Folder Structure — Complete Guide Enterprise State Architecture — Complete Guide Enterprise Form Architecture — Complete Guide Actions — Complete Guide use() — Complete Guide Suspense — Complete Guide Concurrent Rendering — Complete Guide React Compiler — Complete Guide Server Components — Complete Guide Streaming Rendering — Complete Guide
Module 7: Performance Hydration — Complete Guide Memoization — Complete Guide React.memo — Complete Guide Lazy Loading — Complete Guide Code Splitting — Complete Guide Virtualization — Complete Guide Bundle Optimization — Complete Guide Web Vitals — Complete Guide Frontend Performance Tuning — Complete Guide Micro Frontends — Complete Guide
Module 8: Full-Stack & Real-Time Enterprise Scaling — Complete Guide SignalR — Complete Guide WebSockets — Complete Guide SSE — Complete Guide Next.js — Complete Guide SSR — Complete Guide SSG — Complete Guide ISR — Complete Guide ASP.NET Core Integration — Complete Guide Full-stack Enterprise Architecture — Complete Guide
Module 9: Testing & Deployment XSS Protection — Complete Guide Secure Authentication — Complete Guide Jest — Complete Guide React Testing Library — Complete Guide Cypress — Complete Guide Playwright — Complete Guide Docker Deployment — Complete Guide Kubernetes — Complete Guide Azure Deployment — Complete Guide CI/CD Pipelines — Complete Guide
Module 10: ShopCart Projects Todo App Project — Complete Guide E-Commerce Storefront Project — Complete Guide SaaS Admin Panel Project — Complete Guide Banking Dashboard Project — Complete Guide LMS Course Player Project — Complete Guide Healthcare Portal Project — Complete Guide Real-Time Monitoring Project — Complete Guide Multi-Tenant SaaS Project — Complete Guide Enterprise CRM Project — Complete Guide Micro Frontend Platform Project — Complete Guide
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