#8 Javascript Arrays | Javascript Hindi Course For Beginners ( 2023 )
An array in JavaScript is a data structure that allows you to store multiple values in a single variable. It's like a list of items, where each item can be accessed by its index (position) in the list. The items in an array can be of any data type, including numbers, strings, objects, and other arrays. Arrays are a useful tool for organising and manipulating data in a program.
CRUD Operation Array
How loop over array
Array Methods
Array Checker Methods
Questions
question 1
Concatenate Variable Number of Input Arrays
Create a function that concatenates n input arrays, where n is variable.
@helen_yu
Question 2
Store Payment
Given a total due and an array representing the amount of change in your pocket.
determine whether or not you are able to pay for the item.
Change will always be represented in the following order: ₹1 coin, ₹2 coin, ₹5 coin, ₹10 coin
changeEnough([25, 20, 5, 5], 120) should yield true
@helen_yu
since having 25 → ₹1 coin, 20 → ₹2 coin, 5 → ₹5 coin and 5 → ₹10 coin
gives you 25 + 40 + 25 + 50 = 140
Question 3
Factorial of number using reduce method
factorial of 4 = 1*2*3*4 = 24
Question 4
Find the Second Largest Number
Create a function that takes an array of numbers and returns the second largest
number. @matt
// Example of Array
let daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
//Array is index value pair.
// index of array start from 0
// we can also write array as object
let daysOfWeek = {
0: 'Sunday',
1: 'Monday',
2: 'Tuesday',
3: 'Wednesday',
4: 'Thursday',
5: 'Friday',
6: 'Saturday'
};
// Inside array we can store any data we want. like boolean , string
// number , array ,objects
// CREATE
let daysOfWeek = []
daysOfWeek.push('Sunday') // add at end
daysOfWeek.push('Monday')
daysOfWeek.unshift("START1","START2" ) // add at starting
// So on .......
// READ
let daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
const sunday = daysOfWeek[0]
// UPDATE
daysOfWeek[0] = "Unkown"
// DELETE
daysOfWeek.pop() // removes last element -> FRIDAY
daysOfWeek.shift() // removes first element -> Sunday
daysOfWeek.splice(3, 1); // removes the element at index 3 (Wednesday)
daysOfWeek.slice(2); // removes first two elements
// but does not modify same array
// removes array elements which don't fit in condition
const filteredDay = daysOfWeek.filter(word => word.length > 6);
let daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
// Simple for loop
for (let i = 0; i < daysOfWeek.length; i++) {
let day = daysOfWeek[i];
console.log(`Today is ${day}`);
}
// Using for of loop
for (let day of daysOfWeek) {
console.log(`Today is ${day}`);
}
// using forEach loop -> forEach loop does't writtern any array
// there are three parameters -> value , currentIndex , fullArray
daysOfWeek.forEach((day,index,array) => {
console.log(`Today is ${day}`);
console.log(`Day ${index}`);
console.log(array);
});
// using map loop -> map loop return new array
let messages = daysOfWeek.map(day => `Today is ${day}`);
console.log(messages);
// Array.prototype.find()
// For Searching element in array
const array1 = [5, 12, 8, 130, 44];
const found = array1.find(element => element > 10);
console.log(found);
// Expected output: 12
// Array.prototype.indexOf()
// For search index of element
const beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];
console.log(beasts.indexOf('bison'));
// Expected output: 1
// Start from index 2
console.log(beasts.indexOf('bison', 2));
// Expected output: 4
console.log(beasts.indexOf('giraffe'));
// Expected output: -1
// Array.prototype.findIndex()
// // For search index of element based on condiiton
const array1 = [5, 12, 8, 130, 44];
const isLargeNumber = (element) => element > 13;
console.log(array1.findIndex(isLargeNumber));
// Expected output: 3
// Array.prototype.at()
// getting value of element using index of element
const array1 = [5, 12, 8, 130, 44];
let index = 2;
console.log(`Using an index of ${index} the item returned is ${array1.at(index)}`);
// Expected output: "Using an index of 2 the item returned is 8"
index = -2;
console.log(`Using an index of ${index} item returned is ${array1.at(index)}`);
// Expected output: "Using an index of -2 item returned is 130"
// Array.prototype.every()
// every condition is true then it will return true
// otherwise false
const isBelowThreshold = (currentValue) => currentValue < 40;
const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every(isBelowThreshold));
// Expected output: true
// Array.isArray()
// For checking current variable is object or not
console.log(Array.isArray([1, 3, 5]));
// Expected output: true
console.log(Array.isArray('[]'));
// Expected output: false
// Array.prototype.some()
// for some element will safisfy condition then it will return true
const array = [1, 2, 3, 4, 5];
// Checks whether an element is even
const even = (element) => element % 2 === 0;
console.log(array.some(even));
// Expected output: true
// Array.prototype.includes()
// if elements exist inside array then it will return true
const array1 = [1, 2, 3];
console.log(array1.includes(2));
// Expected output: true
const pets = ['cat', 'dog', 'bat'];
console.log(pets.includes('cat'));
// Expected output: true
console.log(pets.includes('at'));
// Expected output: false
// Array.prototype.reduce()
// it will combine array // based on some operation
const array1 = [1, 2, 3, 4];
// 0 + 1 + 2 + 3 + 4
const initialValue = 0;
const sumWithInitial = array1.reduce(
(accumulator, currentValue) => accumulator + currentValue,
initialValue
);
console.log(sumWithInitial);
// Expected output: 10
// Array.prototype.join()
// it will combine elements together
const elements = ['Fire', 'Air', 'Water'];
console.log(elements.join());
// Expected output: "Fire,Air,Water"
console.log(elements.join(''));
// Expected output: "FireAirWater"
console.log(elements.join('-'));
// Expected output: "Fire-Air-Water"
// Array.prototype.reverse()
// it will just reverse order of elements
const array1 = ['one', 'two', 'three'];
console.log('array1:', array1);
// Expected output: "array1:" Array ["one", "two", "three"]