Complete MERN Stack 90-Day Course Roadmap: Your Journey from Beginner to Job-Ready Developer

Week 5: Advanced JavaScript & DOM Power (Days 31-37)

Day 31-32: DOM Manipulation Fundamentals

The Document Object Model (DOM) is what connects JavaScript to your HTML pages. Think of the DOM as a bridge that lets your JavaScript code talk to and control everything on your webpage. You learn querySelector and querySelectorAll to find elements, innerHTML and innerText to change content, and how to create, modify, and delete elements dynamically. 

Your practice project involves creating a dynamic product catalog where clicking buttons adds items to a shopping cart display, updates quantities, and calculates totals—all without refreshing the page. This hands-on work shows you how modern websites feel so interactive and responsive. 

Day 33-34: DOM Traversal and Events

DOM traversal lets you navigate between parent elements, child elements, and sibling elements like moving through a family tree. You master parentElement, children, nextElementSibling, and previousElementSibling properties. 

Event handling transforms static pages into interactive experiences. You learn addEventListener for clicks, form submissions, keyboard inputs, mouse movements, and touch events. Understanding event handling is crucial because every interactive element on websites—from dropdown menus to image sliders—relies on these concepts. 

Your assignment: build an image gallery with previous/next buttons, keyboard navigation, and hover effects that highlight images. 

Day 35: DOM Attributes and Local Storage

DOM attributes control how elements behave and appear. You learn to get, set, and remove attributes like src, href, disabled, and data attributes. Local Storage lets you save data in the browser so users don’t lose information when they refresh or close the page. 

Today’s practical project involves creating a theme switcher that remembers user preferences (dark mode or light mode) even after closing the browser, and a note-taking app that saves notes locally. 

Day 36-37: Sorting, Filtering, and Advanced Array Methods

Real applications constantly need to organize and filter data. You master different sorting techniques (bubble sort, selection sort), understand time complexity basics, and practice sorting objects by different properties. You also deepen your knowledge of filter, map, reduce, and combining these methods for complex data transformations. 

Weekend challenge: build a product filtering system where users can sort by price (high to low, low to high), filter by category, search by name, and see results update instantly. 

Week 5 Milestone: You can now create fully interactive web pages that respond to user actions and save data locally. 

Week 6: Asynchronous JavaScript Mastery (Days 38-44)

Day 38-39: Understanding JavaScript Execution

JavaScript’s asynchronous nature confuses many beginners. You learn the difference between synchronous and asynchronous code, how JavaScript actually works under the hood, the call stack, Web APIs provided by browsers, and the event loop that coordinates everything. 

Understanding these concepts separates junior developers who copy code from professionals who understand why code behaves the way it does. You practice with setTimeout, setInterval, and real-world examples showing why asynchronous programming matters. 

Day 40-41: Promises and Modern Async Programming

Promises revolutionized JavaScript programming by making asynchronous code more manageable. You learn promise creation, .then() and .catch() methods, promise chaining, Promise.all() for handling multiple async operations, and the modern async/await syntax that makes asynchronous code look synchronous. 

Your projects include creating a delayed notification system, fetching multiple APIs simultaneously and combining results, and building an image loader that shows loading states. 

Day 42-43: Fetch API and Working with External Data

The Fetch API connects your applications to the entire internet. You learn GET requests to retrieve data, POST requests to send data, PUT and DELETE for updates and deletions, handling JSON data, error handling, and working with API authentication. 

Real-world exercise: build a weather application that fetches real-time weather data from OpenWeatherMap API, displays it beautifully, handles loading states, and manages errors gracefully. This project mimics what you’ll do in actual development jobs. 

Day 44: ES6 Advanced Features

You continue mastering modern JavaScript features including different loop types (for…of, for…in, forEach), arrow function nuances, object shorthand syntax, the difference between statements and expressions, lexical scope, let vs var vs const behavior, destructuring arrays and objects efficiently, hoisting behavior, Immediately Invoked Function Expressions (IIFE), and the often-confusing ‘this’ keyword. 

Practice involves refactoring older JavaScript code using these modern patterns, making your code cleaner, shorter, and more professional. 

Week 6 Milestone: You understand asynchronous JavaScript and can fetch and manipulate data from external APIs. 

Week 7: JavaScript Prototypes & Advanced Projects (Days 45-51)

Day 45-46: Classical and Prototypal Inheritance

JavaScript’s inheritance system works differently from traditional programming languages. You learn classical inheritance concepts, prototype chains, creating custom prototype chains, Object.assign vs Object.setPrototypeOf, and how to chain methods using functions’ prototype objects. 

You explore three ways to create objects: factory functions, constructor functions, and ES6 classes. Understanding these patterns helps you read and work with any JavaScript codebase. 

Day 47-48: Advanced Object Creation and the ‘new’ Keyword

You dive deeper into prototypal inheritance using different object creation patterns, understand problems that arise with the ‘new’ keyword, and learn best practices for object-oriented programming in JavaScript. These concepts appear frequently in technical interviews and real-world codebases. 

Projects include building a class hierarchy (like Vehicle → Car → ElectricCar) with shared and specific methods, demonstrating inheritance in action. 

Day 49-50: DOM CRUD Operations and JWT Authentication

You build a complete application with Create, Read, Update, and Delete operations using DOM manipulation. You also learn about JWT (JSON Web Tokens) for authentication, understanding how modern web applications manage user login sessions securely. 

The major project: create a personal diary application where users can add entries, edit existing ones, delete entries, and search through them—with JWT authentication protecting the data. 

Day 51: Advanced DOM Concepts and Testing

Event bubbling and capturing determine the order in which events trigger on nested elements. Understanding these concepts prevents common bugs in interactive applications. You also implement pagination for large datasets, breaking information into manageable pages. 

Introduction to JEST testing teaches you how professional developers ensure code quality. Writing tests seems tedious initially, but it becomes essential as applications grow complex. You learn basic test writing and understand why testing matters in production codebases. 

Week 7 Milestone: You’ve completed JavaScript Level 3 with professional-grade projects showcasing advanced concepts. 

Week 8: React.js Fundamentals (Days 52-60)

Day 52-53: React Introduction and Setup

React transformed how developers build user interfaces. You understand what React is, why Facebook created it, how it differs from vanilla JavaScript, and why companies worldwide prefer it. You learn about Babel (the transpiler that converts modern JavaScript), set up your development environment, and create your first React application. 

Key concepts include components (reusable UI pieces), props (passing data between components), JSX syntax (writing HTML-like code in JavaScript), and the Virtual DOM (React’s secret to fast performance). Your first project: build a simple component-based layout with header, sidebar, and content sections. 

Day 54-55: Conditional Rendering and Lists

Real applications show different content based on conditions and frequently display lists of data. You master conditional rendering techniques (using if-else, ternary operators, and logical && in JSX), rendering lists with map(), understanding the importance of keys for performance, and creating dynamic component layouts. 

Projects include a product showcase that displays different badges (Sale, New, Featured) based on conditions, and a user directory that renders from an array of user objects. 

Day 56-57: Component Architecture and Styling

Professional React applications organize components intelligently. You learn import and export patterns (default exports vs named exports), understand Single Page Applications (SPA), discover how the Virtual DOM optimizes performance, and implement both Global CSS and CSS Modules for styling. 

Understanding component architecture prevents your codebase from becoming messy and unmaintainable. You practice breaking a complex UI mockup into reusable components. 

Day 58-59: State Management and Interactive Components

State is what makes React components dynamic and interactive. You learn the useState hook, understand the difference between props (passed from parent) and state (managed internally), handle synthetic events (React’s cross-browser event system), and build truly interactive components. 

Projects include creating a counter with increment/decrement buttons, a form with controlled inputs, and a toggle switch component. These seemingly simple projects teach fundamental patterns you’ll use constantly. 

Day 60: API Requests and Component Communication

Components need to share data and communicate with each other. You learn state upliftment (moving state to parent components), component communication patterns, making API requests in React, and displaying fetched data. 

Your weekend challenge: build a multi-component application where a search bar in one component filters results displayed in another component, with data fetched from an API. 

Month 2 Milestone: You’ve transitioned from vanilla JavaScript to React, understanding component-based architecture and state management.