Wondering how to store values in JavaScript without hitting ""undefined is not a function"" every five minutes? This module answers exactly that question. By the end of this module you will declare variables correctly with let and const and diagnose a type-related bug from the error message alone. You'll compare let, const, and var, work with the core data types — string, number, boolean, null, undefined, object, symbol — read a stack trace in the browser DevTools console, and step through code with breakpoints in VS Code or WebStorm. This module is designed for beginners who can already run a JavaScript file and now want their code to stop breaking for reasons they can't explain, and for career switchers who need to read error output the way a working developer does. No prior debugging experience is required, and everything runs in the free browser DevTools and a free editor. Along the way you'll see why JavaScript converts types behind your back, what == does that === does not, and which modern code-style rules prevent whole categories of variable bugs before they happen. You'll finish with a debugging checklist and a set of annotated error examples you can reuse whenever a script fails, in this course or in your own projects.

Wondering how to make JavaScript decide something instead of just running top to bottom? This module answers exactly that question. By the end of this module you will write a script that branches on conditions and repeats over a set of data. You'll build conditions with if, else if, else, and switch, write for, while, and do...while loops, use the ternary operator for short decisions, and control iteration precisely with break and continue. This module is designed for beginners who can declare variables and now need real logic, and for anyone automating a repetitive task who wants the script to handle every case rather than one. No prior programming background is required, and every example runs in the browser console or in Node.js on any operating system. Along the way you'll learn which values JavaScript treats as truthy and falsy, why == and === behave differently inside a condition, and how to avoid the infinite loop that catches almost every beginner once. You'll finish with a working contact list script — add, search, and delete entries — plus a starter file you can extend into a larger tool, ready to reuse as the data layer of your first real application.

Wondering how to store a list of users, products, or tasks in JavaScript and then filter it? This module answers exactly that question. By the end of this module you will transform a realistic dataset using array methods and object operations. You'll create and index arrays, add and remove items with push, pop, and splice, reshape data with map, filter, and reduce, loop with for...of and for...in, and add, update, and delete properties on objects. This module is designed for beginners who can already write loops and conditions and now need somewhere to put their data, and for analysts or marketers who want to process records in JavaScript instead of by hand. No prior experience with data structures is required, and all code runs in the browser console or in Node.js. Along the way you'll learn when an array is the right shape for your data and when an object is, why sorting and searching behave the way they do, and how to chain array methods without creating unreadable code. You'll finish with a live password strength checker built from your own array logic — length, uppercase, numbers, and special characters — plus a reusable data-handling snippet set, ready to drop into any future project.

Wondering how to stop copying the same five lines of JavaScript into every file? This module answers exactly that question. By the end of this module you will refactor duplicated code into parameterised, reusable functions. You'll declare functions and call them, pass arguments and set default values, return results instead of printing them, write function expressions, and convert them into concise ES6 arrow functions. This module is designed for beginners who can already write loops and work with arrays, and for professionals automating tasks who want a small personal library of helpers rather than one long script. No prior experience with functional programming is required, and every example runs in the browser console or in Node.js. Along the way you'll learn what scope means in practice, why a function declaration is available before it appears in the file while a function expression is not, what return actually gives back to the caller, and when an arrow function is the better choice. You'll finish with a set of working utility functions — formatDate, calculateTip, and validateEmail — plus a refactored version of an earlier script, ready to reuse as the helpers file in every project you build next.

Wondering how to make a button on a web page actually do something when a visitor clicks it? This module answers exactly that question. By the end of this module you will change what a page shows in response to a user action. You'll read the DOM tree the browser builds from your HTML, select elements with querySelector, querySelectorAll, and getElementById, edit text, attributes, and classes from JavaScript, and attach behaviour with addEventListener for click and input events. This module is designed for beginners who can write functions and now want visible results in a browser, and for designers or marketers who need a page to react without waiting on a developer. No framework is required — no React, no jQuery — and the supplied HTML and CSS starter files mean no front-end experience is assumed. Along the way you'll learn why the DOM is a live tree rather than your source file, how an event travels through the page, and why attaching listeners in JavaScript is safer than writing onclick directly in HTML. You'll finish with an interactive page containing a working counter, a dark-mode toggle, and a like button, ready to publish as the first piece of your developer portfolio.

Wondering how to make JavaScript wait for something slow without freezing the whole page? This module answers exactly that question. By the end of this module you will write a script that handles a delayed result without blocking execution. You'll schedule code with setTimeout and setInterval and clear them cleanly, create and chain promises with .then() and .catch(), and rewrite the same logic with async and await so it reads top to bottom. This module is designed for beginners who can write functions and manipulate the DOM and now need to work with data that arrives later, and for anyone preparing to call an API or a database from JavaScript. No prior experience with asynchronous programming is required, and every example runs in the browser console or in Node.js. Along the way you'll learn what the event loop does with your code, why a promise result cannot be read on the next line, how errors behave differently inside asynchronous functions, and when a plain callback still makes sense. You'll finish with a working asynchronous tool — a countdown plus a delayed data fetch handled with async/await — and an error-handling pattern you can reuse for every API call you write from here on.

Wondering how to combine everything you know into one JavaScript project you can show an employer? This module answers exactly that question. By the end of this module you will build and ship a complete to-do list application in plain JavaScript. You'll structure the app's data as an array of objects, render it into the DOM, wire up add, edit, delete, and mark-as-done with event listeners, and organise the code into named functions instead of one long file. This module is designed for learners who have covered variables, loops, functions, the DOM, and asynchronous basics and now want a finished artefact, and for career switchers who need a portfolio piece before their first application. No framework and no build tools are required — the whole project runs from an HTML file in any browser. Along the way you'll see how the pieces fit together in a real app, what a reviewer looks for in naming and file structure, and which next step — modern ES6+, React, Vue, or Node.js with Express — makes sense once this project is done. You'll finish with a working to-do list app and a written README, ready to link from your CV, your GitHub profile, or your first developer job application.