Soa Technology

5️⃣ Arrays in JavaScript

—

by

aditya singh
in

📌 What is an Array?

An array is a collection of values stored in a single variable.

let fruits = ["Apple", "Banana", "Mango"];

🛠️ Creating Arrays

1. Using []

let numbers = [10, 20, 30];

2. Using Array constructor

let numbers = new Array(10, 20, 30);

🎯 Accessing Elements

let fruits = ["Apple", "Banana", "Mango"];console.log(fruits[0]); // Apple
console.log(fruits[1]); // Banana

👉 Index starts from 0

⚙️ Basic Array Methods

➕ push() → Add at end

let arr = [1, 2];
arr.push(3);console.log(arr); // [1, 2, 3]

➖ pop() → Remove from end

let arr = [1, 2, 3];
arr.pop();console.log(arr); // [1, 2]

⬅️ shift() → Remove from start

let arr = [1, 2, 3];
arr.shift();console.log(arr); // [2, 3]

➡️ unshift() → Add at start

let arr = [2, 3];
arr.unshift(1);console.log(arr); // [1, 2, 3]

✂️ splice() → Add/Remove/Replace

let arr = [1, 2, 3, 4];// remove 2 elements from index 1
arr.splice(1, 2);console.log(arr); // [1, 4]

👉 Add elements:

let arr = [1, 4];
arr.splice(1, 0, 2, 3);console.log(arr); // [1, 2, 3, 4]

🍰 slice() → Copy part of array

let arr = [1, 2, 3, 4];let newArr = arr.slice(1, 3);console.log(newArr); // [2, 3]

👉 Original array does not change

🚀 Advanced Methods

🔁 map() → Transform array

let numbers = [1, 2, 3];let result = numbers.map(num => num * 2);console.log(result); // [2, 4, 6]

🔍 filter() → Select elements

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

➕ reduce() → Single value result

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

🔄 forEach() → Loop through array

let fruits = ["Apple", "Banana"];fruits.forEach(fruit => {
    console.log(fruit);
});

🧠 Practice Projects

🧑‍🎓 1. Student Marks System

let marks = [80, 75, 90, 60];// total marks
let total = marks.reduce((sum, m) => sum + m, 0);// average
let avg = total / marks.length;// passed students (>= 70)
let passed = marks.filter(m => m >= 70);console.log("Total:", total);
console.log("Average:", avg);
console.log("Passed:", passed);

✅ 2. Todo List

let todos = [];// add task
function addTask(task) {
    todos.push(task);
}// remove last task
function removeTask() {
    todos.pop();
}// show tasks
function showTasks() {
    todos.forEach((task, index) => {
        console.log(index + ": " + task);
    });
}// usage
addTask("Study JS");
addTask("Practice Arrays");
showTasks();removeTask();
showTasks();
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