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Arrays

Arrays are ordered collections of values in JavaScript. They can hold multiple items of any type, including numbers, strings, objects, or even other arrays.

Illustration of arrays
Illustration of arrays

💡 What is an Array?

An array groups multiple values under a single variable name, accessible by their index positions starting from 0.

Creating Arrays

  • let arr = []; — creates an empty array
  • let fruits = ['Apple', 'Banana', 'Cherry']; — array with initial values
  • let mixed = [1, 'two', true]; — arrays can hold mixed types

Accessing Array Elements

Use square brackets with an index to access an element:

📌 Deep Dive: Accessing Elements

JAVASCRIPT
const fruits = ['Apple', 'Banana', 'Cherry'];
console.log(fruits[0]); // Apple
console.log(fruits[2]); // Cherry
Output
Apple
Cherry

Common Array Properties and Methods

Useful Array Properties & Methods
Property/MethodDescription
lengthReturns the number of elements in the array
push(value)Adds one or more elements to the end
pop()Removes and returns the last element
shift()Removes and returns the first element
unshift(value)Adds elements to the start
indexOf(value)Returns the index of the first occurrence of a value, or -1 if not found

Modifying Arrays

Arrays are mutable, so you can change elements by index or add/remove items:

📌 Deep Dive: Modifying Arrays

JAVASCRIPT
const colors = ['Red', 'Green', 'Blue'];
colors[1] = 'Yellow'; // Change 'Green' to 'Yellow'
colors.push('Purple'); // Add 'Purple' to the end
console.log(colors);
Output
["Red", "Yellow", "Blue", "Purple"]

⚠️ Remember

Array indices start at 0, so the first element is at array[0] not array[1].

Arrays vs Objects

Arrays are meant for ordered lists accessed by numeric index, while objects store unordered key-value pairs.

Arrays vs Objects
FeatureArraysObjects
StorageOrdered list of valuesKey-value pairs
AccessBy numeric indexBy key (string or symbol)
Use CaseLists, collectionsNamed properties, records
Example['a', 'b', 'c']{a: 1, b: 2}

Multidimensional Arrays

Arrays can contain other arrays, creating a grid or matrix structure:

📌 Deep Dive: Multidimensional Arrays

JAVASCRIPT
const grid = [
  [1, 2],
  [3, 4]
];
console.log(grid[0][1]); // 2
console.log(grid[1][0]); // 3
Output
2
3

💡 Index Out of Bounds

Accessing an index that does not exist returns undefined without an error.

Summary

  • Arrays hold ordered collections accessible by zero-based indexes.
  • They can store any data type and are mutable.
  • Common methods include push, pop, and length.
  • Arrays are ideal for lists, while objects are better for named properties.
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