JavaScript

What's inside

Lessons go from the basics to advanced topics. Read them in order, or jump to what you need.

1. 01

   Chapter 1

   Getting Started

   • 1JavaScript IntroductionJavaScript is the programming language of the web. It makes pages interactive, and with Node.js it also runs outside the browser.
   • 2Where to Write JavaScriptJavaScript goes inside a <script> tag or in an external .js file. Learn where to place it and why the defer attribute matters.
   • 3JavaScript OutputDisplay results with console.log(), write them into page elements with textContent or innerHTML, or show a quick message with alert().
   • 4JavaScript SyntaxLearn the rules for writing JavaScript: statements, semicolons, case sensitivity, identifiers and code blocks.
   • 5JavaScript CommentsComments explain your code and are ignored when the program runs. Use // for a single line and /* */ for several lines.
2. 02

   Chapter 2

   Variables & Data

   • 6JavaScript VariablesVariables are named containers for data. Learn to declare them with let and const, and understand the old var and why we avoid it.
   • 7JavaScript Data TypesJavaScript has seven primitive data types plus objects. Get to know them, and use the typeof operator to check the type of any value.
   • 8JavaScript OperatorsOperators perform actions on values: arithmetic, assignment, comparison and logical operators, plus the modern ?? and ?. operators.
   • 9JavaScript StringsStrings store text. Learn about quotes, template literals, escape characters and the length property.
   • 10String MethodsBuilt-in string methods let you search, cut, change case, trim and split text. Here are the ones you'll use every day.
   • 11Numbers and MathJavaScript has one number type for both integers and decimals. Learn about decimal precision, toFixed(), converting strings to numbers, NaN and the Math object.
   • 12Booleans and ComparisonsA boolean is either true or false. Learn which values are truthy or falsy, and why you should use === instead of ==.
3. 03

   Chapter 3

   Control Flow

   • 13if...else StatementsUse if, else if and else to run different code depending on conditions, and the ternary operator for short decisions.
   • 14The switch StatementThe switch statement compares one value against many possible cases. It's a tidy alternative to long else if chains.
   • 15The for LoopThe for loop repeats code a set number of times. It's perfect for counting and for going through arrays.
   • 16while and do...while Loopswhile repeats code as long as a condition is true, and do...while always runs at least once. Control any loop with break and continue.
   • 17for...of and for...infor...of loops over the values of arrays and strings, while for...in loops over the keys of an object.
4. 04

   Chapter 4

   Functions

   • 18JavaScript FunctionsFunctions are reusable blocks of code. Learn to declare them, pass parameters, set default values and return results.
   • 19Arrow FunctionsArrow functions are a shorter way to write functions with =>. You'll find them everywhere in modern JavaScript, especially with array methods.
   • 20Scope and ClosuresScope decides where a variable can be used: block, function or global scope. Closures let functions remember the variables from the scope where they were created.
5. 05

   Chapter 5

   Arrays & Objects

   • 21JavaScript ArraysArrays store ordered lists of values. Learn to create them, access items by index, and add, remove, find and sort items.
   • 22Array Methods: map, filter, reduceWork with arrays like a pro using forEach, map, filter, reduce, find, some and every, with practical examples based on student grades.
   • 23JavaScript ObjectsObjects group related data and behavior into key-value pairs. Learn about properties, methods, this, and how to loop over objects.
   • 24Destructuring and SpreadDestructuring unpacks values from arrays and objects into variables. The spread operator ... copies and merges values, and the rest syntax collects them.
   • 25JavaScript JSONJSON is the standard text format for exchanging data. Convert objects to JSON with JSON.stringify() and back with JSON.parse().
6. 06

   Chapter 6

   The Browser

   • 26The HTML DOMThe DOM is JavaScript's live model of the page. Learn to select elements, change their text, HTML, styles and classes, and create new elements.
   • 27JavaScript EventsEvents let your code react to users. Use addEventListener() for clicks, typing and form submissions, read the event object, and meet event delegation.
   • 28Forms and ValidationRead values from form fields, validate them with JavaScript, show helpful error messages, and stop invalid submissions with preventDefault().
7. 07

   Chapter 7

   Modern JavaScript

   • 29JavaScript ClassesClasses are templates for creating objects. Learn about the constructor, methods, inheritance with extends and super, and getters.
   • 30Error HandlingHandle errors gracefully with try, catch and finally, create your own errors with throw, and learn the common error types.
   • 31Promises and async/awaitHandle tasks that take time without freezing the page. Learn setTimeout, promises with then and catch, and the cleaner async/await syntax.
   • 32The Fetch APIUse fetch() with async/await to load JSON data from a server, check the response, and handle network errors properly.