- 01Setting Up (What You'll Need)
- 02Creating Variables
- 03Conditionals (if Statements)
- 04Loops (for Statements)
- 05Creating Functions
- 06Working with Arrays
- 07Working with Objects
- 08Loops (while Statements)
- 09Working with Strings
- 10Using Classes (Object-Oriented Programming)
- 11Error Handling (try...catch)
- 12Destructuring and the Spread Syntax
- 13Async Code (Promise / async & await)
- 14Advanced Array Methods (filter and reduce)
- 15The switch Statement
- 16The Ternary Operator
- 17Inheritance (Extending Classes)
- 18How to Write Comments
- 19Logical Operators (AND, OR, NOT)
- 20Constants (Making Read-Only Values with const)
- 21Splitting and Joining Strings (split and join)
- 22Null-Safe Syntax (?? and ?.)
- 23Searching Arrays and Collections (includes and find)
- 24Transforming Arrays with map
- 25Two-Dimensional Arrays (Table-Shaped Data)
- 26Building a Custom Error Class
- 27Default Arguments (Setting Initial Values for Parameters)
- 28Using Set (Collections)
- 29Verifying Correctness with assert (Your First Step Into Testing)
- 30Higher-Order Functions (Passing a Function as an Argument)
- 31Stacks and Queues (Basic Data Structures)
- 32The Basics of Type Conversion (Casting)
- 33Introduction to Regular Expressions (Pattern Matching)
- 34The Binary Search Algorithm
- 35Building a Caesar Cipher (a Letter-Shifting Cipher)
- 36Understanding How Bubble Sort Works
- 37Building and Displaying Dates (Basic Year/Month/Day Operations)
- 38Writing Several Unit Tests Together (Multiple Test Cases)
- 39Speeding Up Calculations with Memoization (Caching)
- 40Normalizing Strings (trim and Case Unification)
- 41The Difference Between Shallow Copy and Deep Copy
- 42The Basics of Enums (Enumerated Types)
- 43Flattening Arrays (flatten)
- 44Reversing a String and Checking for a Palindrome
- 45Pairing Up Two Arrays (a zip Operation)
- 46Rounding Numbers (floor, ceil, and round)
- 47Multi-Line Strings (Template Literals)
- 48Returning Multiple Values from a Function (Array Destructuring)
- 49Finding the GCD and LCM (the Euclidean Algorithm)
- 50Formatting Numbers (Digit Alignment and Decimal Precision)
- 51Cleanup Processing with try/catch/finally
- 52Writing Type-Agnostic, General-Purpose Functions
- 53The Basics of Map (an Object for Key-Value Pairs)
- 54Generating Random Numbers
- 55Bitwise Operations (AND, OR, XOR, and Shift Operations)
- 56Using static (Static Class Properties and Methods)
- 57Waiting a Fixed Amount of Time (setTimeout and await)
- 58Watch Out for Floating-Point Rounding Error
- 59Transforming and Flattening at Once with flatMap()
- 60FizzBuzz (the Classic Practice Problem)
- 61Checking Whether a Number Is Prime
- 62Set Operations with Set (Union, Intersection, and Difference)
- 63Converting Number Bases (Binary and Hexadecimal)
- 64Checking That Brackets Match (an Application of Stacks)
- 65Checking for an Anagram
- 66Checking Whether a Year Is a Leap Year
- 67Converting Temperature (Celsius ⇄ Fahrenheit)
- 68Finding the Prime Factorization
- 69[Applied] Build a Simple To-Do List Tool
Using Classes (Object-Oriented Programming)
In this lesson you'll learn the basics of object-oriented programming using JavaScript's class syntax, so you can handle data that shares common characteristics together. This is for people searching "JavaScript class usage" or "JavaScript what is a constructor."
A class is a "blueprint" for objects that share similar characteristics. You define a class with class, and use new to create an actual object (an instance) from that blueprint. Imagine an "animal blueprint" that lets you create as many concrete instances as you like — "dog," "cat," and so on. The constructor is a special method called first whenever an instance is created, used to set up its initial state.
The sample code gives the Animal class two properties, name and sound, and builds a sound message using a method called speak(). Writing new Animal("Dog", "Woof") creates a single instance (dog) holding that information, and dog.speak() calls the processing that's specific to that instance.
A common beginner stumbling block is understanding what this refers to. Inside a class, this refers to "the very instance currently being created," but that's easy to find confusing until you get used to it. Also remember that trying to call a class without new results in an error.
In real development, designing data that represents a "thing" — a user, a product, an order — as a class is the basic idea behind object orientation. The larger the application, the more the quality of this kind of class design affects the maintainability of the entire codebase, which is why it's taken seriously in real projects.
A class can have any number of methods added to it — not just "make a sound," but also behaviors like "eat" and "walk" can all be defined together. Bundling related data (properties) and processing (methods) into a single class makes your code easier to follow and easier to reuse.
Classes also have a mechanism called "private fields" for properties you don't want changed directly from outside the class. Prefixing a property name with # makes it inaccessible from outside the class, enabling safer class design.
💡 Anything passed to console.log() appears in the output below.