- 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
Destructuring and the Spread Syntax
In this lesson you'll master destructuring and the spread syntax in JavaScript so you can efficiently pull values out of, or combine, objects and arrays. This is for people searching "JavaScript destructuring usage" or "JavaScript spread syntax."
Destructuring lets you pull values out of an object or array all at once. Writing const { name, age } = user; extracts user.name and user.age into two separate variables in a single step. The spread syntax (...) is used to expand and copy, or combine, arrays and objects. Both are modern styles that show up constantly in real-world code.
The sample code destructures name and age out of the object user, and expands the array nums with the spread syntax to build a new array, newNums, with extra elements added. Values that used to take several lines to extract one at a time can now be pulled out in a single line, making code more readable and dramatically cutting down how much you have to write.
A common beginner stumbling block is that the names you use in destructuring must match the original property names. Specifying a property name that doesn't exist doesn't throw an error — it just becomes undefined. Also be careful: the spread syntax only creates a "shallow copy," so nested objects don't get duplicated all the way down.
In real development, this is now an indispensable notation for writing modern JavaScript — pulling just the values you need out of an object passed as a function argument, or, in a library like React, using the spread syntax to copy existing state before changing just part of it when updating state.
Destructuring also lets you rename the variable you're extracting into. Writing const { name: userName } = user; lets you receive the value of the name property under a different variable name, userName — handy when you want to avoid colliding with the original property name.
Object destructuring also lets you specify a default value at the same time. Writing const { age = 18 } = user; means that if the age property doesn't exist, 18 is automatically used — a mechanism similar to default arguments.
💡 Anything passed to console.log() appears in the output below.