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Arrays-in-JS.md

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What are arrays in JavaScript ?

Arrays in JavaScript are special objects used to store multiple values in a single variable. They allow you to group related data together and provide various methods to manipulate the collection efficiently. Arrays are zero-indexed, meaning the first element has an index of 0.

Key Features of Arrays:

  1. Dynamic Size: Arrays in JavaScript can grow or shrink dynamically as elements are added or removed.
  2. Mixed Data Types: An array can hold elements of different data types, such as numbers, strings, objects, or even other arrays.
  3. Indexed Access: Elements in an array can be accessed using their numeric index.

Declaring Arrays:

There are two main ways to create arrays in JavaScript:

  1. Using Array Literal Syntax: 
    const fruits = ["Apple", "Banana", "Cherry"];
  2. Using the Array Constructor: 
    const numbers = new Array(1, 2, 3, 4);

Accessing Array Elements:

You can access elements using their index:

const fruits = ["Apple", "Banana", "Cherry"];
console.log(fruits[0]); // Output: Apple

Common Array Methods:

  1. push() - Adds an element to the end of the array.

    const fruits = ["Apple", "Banana"];
fruits.push("Cherry");
console.log(fruits); // ["Apple", "Banana", "Cherry"]

  2. pop() - Removes the last element from the array.

    const fruits = ["Apple", "Banana", "Cherry"];
fruits.pop();
console.log(fruits); // ["Apple", "Banana"]

  3. shift() - Removes the first element of the array.

    const fruits = ["Apple", "Banana", "Cherry"];
fruits.shift();
console.log(fruits); // ["Banana", "Cherry"]

  4. unshift() - Adds an element to the beginning of the array.

    const fruits = ["Banana", "Cherry"];
fruits.unshift("Apple");
console.log(fruits); // ["Apple", "Banana", "Cherry"]

  5. slice() - Returns a shallow copy of a portion of the array.

    const fruits = ["Apple", "Banana", "Cherry", "Date"];
const citrus = fruits.slice(1, 3);
console.log(citrus); // ["Banana", "Cherry"]

  6. splice() - Modifies the contents of an array by adding, removing, or replacing elements.

    const fruits = ["Apple", "Banana", "Cherry"];
fruits.splice(1, 1, "Mango");
console.log(fruits); // ["Apple", "Mango", "Cherry"]

  7. map() - Creates a new array by applying a function to each element.

    const numbers = [1, 2, 3];
const squares = numbers.map((num) => num * num);
console.log(squares); // [1, 4, 9]

  8. filter() - Creates a new array with elements that pass a test.

    const numbers = [1, 2, 3, 4];
const even = numbers.filter((num) => num % 2 === 0);
console.log(even); // [2, 4]

  9. reduce() - Reduces an array to a single value.

    const numbers = [1, 2, 3, 4];
const sum = numbers.reduce((acc, num) => acc + num, 0);
console.log(sum); // 10

Multidimensional Arrays:

JavaScript arrays can hold other arrays, creating a multidimensional array:

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];
console.log(matrix[1][2]); // Output: 6

Conclusion:

Arrays are a fundamental data structure in JavaScript that offer flexibility and efficiency in handling collections of data. Their extensive built-in methods make them powerful tools for developers to perform various operations.