#8 Javascript Arrays | Javascript Hindi Course For Beginners ( 2023 )

 // 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

CRUD Operation Array

// 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);

How loop over array

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 Methods

// 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.concat()
// for combining two arrays

const array1 = ['a', 'b', 'c'];
const array2 = ['d', 'e', 'f'];
const array3 = array1.concat(array2);

console.log(array3);
// Expected output: Array ["a", "b", "c", "d", "e", "f"]

// 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.sort()
// for sorting using this method

const months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months);
// Expected output: Array ["Dec", "Feb", "Jan", "March"]

const array1 = [1, 30, 4, 21, 100000];
array1.sort();
console.log(array1);
// Expected output: Array [1, 100000, 21, 30, 4]

// 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"]

Questions

// examples 
concat([1, 2, 3], [4, 5], [6, 7]) ➞ [1, 2, 3, 4, 5, 6, 7]
concat([1], [2], [3], [4], [5], [6], [7]) ➞ [1, 2, 3, 4, 5, 6, 7]
concat([1, 2], [3, 4]) ➞ [1, 2, 3, 4]
concat([4, 4, 4, 4, 4]) ➞ [4, 4, 4, 4, 4]

//examples

changeEnough([10, 6, 5, 2], 69) ➞ false
changeEnough([20, 10, 10, 5], 100) ➞ true

// examples

factorial(1) -> 1
factorial(2) -> 2
factorial(3) -> 6
factorial(4) -> 24

// examples
secondLargest([10, 40, 30, 20, 50]) ➞ 40
secondLargest([25, 143, 89, 13, 105]) ➞ 105
secondLargest([54, 23, 11, 17, 10]) ➞ 23