Javascript Arrays

JavaScript Arrays

An Array in JavaScript is a special variable that holds multiple values in a single reference. Arrays are useful for storing lists of data, and each element in the array has an index, starting from 0.

Declaring Arrays

You can declare an array using square brackets [] or the Array constructor:

let fruits = [“Apple”, “Banana”, “Mango”]; let numbers = new Array(1, 2, 3, 4, 5);

JavaScript Array Methods

JavaScript provides several methods to manipulate arrays:

1. push() – Adds an item to the end of an array.

fruits.push(“Orange”); // Adds “Orange” to the fruits array

2. pop() – Removes the last item of an array.

fruits.pop(); // Removes “Orange”

3. shift() – Removes the first item of an array.

fruits.shift(); // Removes “Apple”

4. unshift() – Adds an item to the beginning of an array.

fruits.unshift(“Strawberry”); // Adds “Strawberry” to the start

5. concat() – Joins two or more arrays and returns a new array.

let tropicalFruits = [“Pineapple”, “Papaya”];

let allFruits = fruits.concat(tropicalFruits);

6. slice() – Returns selected elements in an array as a new array.

let slicedFruits = fruits.slice(1, 3); // Slices from index 1 to 2

7. splice() – Adds/removes items to/from an array at a specified index.

fruits.splice(1, 1, “Kiwi”, “Peach”); // Replaces at index 1

8. join() – Joins all array elements into a string.

let fruitString = fruits.join(“, “);

JavaScript Array Search

There are several methods for searching arrays:

1. indexOf() – Finds the first occurrence of an element.

let position = fruits.indexOf(“Banana”); // Returns index of “Banana”

2. lastIndexOf() – Finds the last occurrence of an element.

position = fruits.lastIndexOf(“Banana”); // Finds last occurrence

3. includes() – Checks if an element exists in the array.

let exists = fruits.includes(“Mango”); // Returns true or false

4. find() – Returns the first element that matches a test function.

let foundFruit = fruits.find(fruit => fruit.length > 5);

5. findIndex() – Returns the index of the first matching element.

let index = fruits.findIndex(fruit => fruit.length > 5);

JavaScript Sorting Arrays

Sorting arrays can be done in ascending or descending order.

1. sort() – Sorts an array alphabetically.

fruits.sort();

2. reverse() – Reverses the elements of an array.

fruits.reverse();

3. Sorting Numbers – Use a compare function with sort() for numeric sorting.

let numbers = [30, 10, 50, 20, 40];

numbers.sort((a, b) => a – b); // Sorts in ascending order

JavaScript Array Iteration

Iteration methods allow you to loop through elements of an array:

1. forEach() – Calls a function for each element in the array.

fruits.forEach(fruit => console.log(fruit));

2. map() – Creates a new array by applying a function to each element.

let fruitLengths = fruits.map(fruit => fruit.length);

3. filter() – Filters the array based on a condition.

let longFruits = fruits.filter(fruit => fruit.length > 5);

4. reduce() – Reduces the array to a single value.

let total = numbers.reduce((sum, value) => sum + value, 0);

5. some() – Checks if some elements meet a condition.

let hasShortFruit = fruits.some(fruit => fruit.length < 5);

6. every() – Checks if all elements meet a condition.

let allLongFruits = fruits.every(fruit => fruit.length > 2);

JavaScript Array Const

Arrays declared with const are still mutable, meaning that you can modify their contents even if the array reference itself is constant:

const cities = [“New York”, “Paris”, “Tokyo”]; cities[0] = “London”; // Allowed cities.push(“Sydney”); // Allowed // However, cities = [“Berlin”, “Madrid”]; // Not allowed

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Javascript Arrays