Array Manipulation in JavaScript: From Basics to Advanced

How do you create an empty array in JavaScript?

const arr = [1, 2, 3, 4, "Hello", {name: "Vishal"}, [1,2,3], 4];
// const arr2 = new Array();
console.log(arr);

How do you access the first and last elements of an array?

const firstElement = arr[0]; // O(1)
const arrLength = arr.length;
const lastElement = arr[arrLength - 1];
console.log(firstElement, arrLength, lastElement);

How do you remove the last element from an array?

const lastElement1 = arr.pop(); // O(1)
console.log(arr, lastElement1);

How do you add an element to the end of an array?

arr.push(5); // O(1)
console.log(arr);

How do you add an element to the start of an array?

arr.unshift(0); // O(N)
console.log(arr);

How do you remove the first element from an array?

arr.shift(); // O(N)
console.log(arr);

How do you loop through an array in JavaScript?

for (let i = 0; i < arr.length; i++){
    console.log(arr[i]);
}

arr.forEach((x, i) => {
    console.log(x);
});

for (let x of arr){
    console.log(x);
}

Question 1: How do you check if an element exists in an array?

const findElement = (arr, target) => {
    for (let x of arr){
        if (x === target){
            return true;
        }
    }
    return false;
}

console.log(findElement(arr, "Hello"));
console.log(findElement(arr, "H"));
console.log(arr.includes("Hello"));

Question 2: How do you find the index of an element in an array?

const findElementIndex = (arr, target) => {
    for (let i = 0; i < arr.length; i++){
        if (arr[i] === target){
            return i;
        }
    }
    return -1;
}

console.log(findElementIndex(arr, "Hello"));
console.log(arr.indexOf("Hello"));

How to delete, add & update elements from a specific index?

console.log(arr);
arr.splice(1, 3);
console.log(arr);
arr.splice(1, 0, 2, 3, 4, 5, 6);
console.log(arr);
arr.splice(1, 3, 6, 7, 8);
console.log(arr);

`splice()` vs `slice()`

const subArr = arr.slice(1, 4); // [start, end)
console.log(subArr);

Shallow Copy of Array

const arrB = arr;
arrB.splice(1, 4);
console.log(arrB, arr);

Deep Copy of Array

const arrC = [...arr];
const arrD = Array.from(arr);
const arrE = arr.concat();
arrC.splice(1, 4);
arrD.splice(1, 4);
arrE.splice(1, 3);
console.log(arrC, arrD, arrE, arr);

How to concatenate two arrays in JavaScript?

const newArr = [...arr, ...arrE];
const newArr2 = arr.concat(arrE);
console.log(newArr, newArr2);

Question 3: How can you check if two arrays are equal?

const isArrayEqual = (arr1, arr2) => {
    if (arr1.length !== arr2.length){
        return false;
    }

    for (let i = 0; i < arr1.length; i++){
        if (arr1[i] !== arr2[i]){
            return false;
        }
    }
    return true;

    // One Line solution
    // return arr1.length === arr2.length && arr1.every((ele, i) => arr1[i] === arr2[i]);
}

console.log(isArrayEqual([1, 2, 3], [1, 2, 3]));

Question 4: How to sort an array in ascending and descending order?

const x = [1, 4, 6, 0, -9, -5];
x.sort(); // O(NlogN)
console.log(x);

x.sort((a, b) => b - a);
console.log(x);

Question 5: How to reverse an array?

x.reverse();
console.log(x);

Map, Filter & Reduce

const newMapArr = x.map((ele, i) => ele * ele);
console.log(newMapArr);

const positiveNumbers = x.filter((ele, i) => ele > 0);
console.log(positiveNumbers);

const sumOFArr = positiveNumbers.reduce((acc, ele) => acc + ele);
console.log(sumOFArr);

Flat: [1, 2, 4, 5, 6, 7, 8, 9]

const y = [1, 2, [4, 5, [6, 7]], 8, 9];
const flattedArray = y.flat(2);
console.log(flattedArray);

`filter()` vs `find()`

const positiveNumber = x.find((ele, i) => ele > 0);
console.log(positiveNumber);

Practice Questions

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