If Array has values of another Arrays so we call it Nested Arrays

let numbers = [1, 2, [3, 4], [5, 6]];

• Main array contains normal values

• It also contains smaller arrays inside it

Nested arrays are common in:

• API responses

• Menu structures

• Categories/subcategories

• Matrix data

• Tree-like structures

Sometimes we need all values in one simple array.

[1, [2, 3], [4, 5]] // nested arrays
[1, 2, 3, 4, 5] // flatten arrays

Flatten Arrays

Flattening converts a nested structure into a single flat list

Approches to convert nested to flatten arrays

1) Using .flat() (modern js)

let arr = [1, 2, [3, 4], [5, 6]]; //nested array 
let result = arr.flat(); // flatten and store on another var
console.log(result); //[1, 2, 3, 4, 5, 6]

.flat() Flatten all levels of arrays

2) Using Loops

let arr = [1, 2, [3, 4]];
let result = [];

for (let i = 0; i < arr.length; i++) {
  if (Array.isArray(arr[i])) {
    result = result.concat(arr[i]);
  } else {
    result.push(arr[i]);
  }
}

console.log(result);

When flattening arrays:

• Check each item

• If normal value → add directly

• If array → take values out

• Repeat until fully flat

3) Using Recursion

function flatten(arr) {
  let result = [];

  for (let item of arr) {
    if (Array.isArray(item)) {
      result = result.concat(flatten(item));
    } else {
      result.push(item);
    }
  }

  return result;
}

console.log(flatten([1, [2, [3, 4]]]));

Summary

Nested arrays = arrays inside arrays
Flattening = converting into one simple array
Use .flat() for easy cases
Learn recursion
Always think step-by-step while solving

Array Basics

• add/remove items

• transform data

• filter values

• calculate totals

• loop through arrays easily

So lets start to deep dive into Array

Array Property .length

let bus = ["0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0"]

console.log(bus.length)// 13 count the items of the array 

Lets discuss about the Arrays methods

.at() and .indexOf are used to the passenger

let friends= ["driver","hitesh","piyush","anirudh","JD"]

console.log(friends.at(2)) //piyush 
//provide the 2nd item (start with 0) 

console.log(friends.indexOf("JD")) //4 
// provide position of item

.fill() and .concat()

let friends= ["driver","hitesh","piyush","anirudh","JD"]

// .fill() used for update all value at once
friends.fill(1) // [1,1,1,1,1]

//.concat() used for add another array value in an array
let fruits =["mango","apple"]

friends.concat(fruits) 
// ["driver","hitesh","piyush","anirudh","JD""mango","apple"]

.push() and .pop()

add and remove items at ends of the array(list)

let friends= ["driver","hitesh","piyush","anirudh","JD"]

console.log(friends.push('another'))// add the last like
//["driver","hitesh","piyush","anirudh","JD","another"]

console.log(friends.pop('another'))// remove from the last like
//["driver","hitesh","piyush","anirudh","JD"]

.unshift() and .shift()

add and remove items at the start of the array(list)

let queue = ["Anu", "Ravi"];

queue.unshift("Priya");   // add to front
console.log(queue);       // ["Priya", "Anu", "Ravi"]

const first = queue.shift();   // remove from front
console.log(first);        // "Priya"
console.log(queue);        // ["Anu", "Ravi"]

.find(), .some(), .every(), .includes(), and .filter()

checking for values like:

• .find() // check for any lady passenger by name

• .some() // check for any lady passenger by boolean

• .every() // check for all passenger is women

• .filter() // give me the ladies passenger list

const passengers = [
{ name: 'Driver', gender: "M", ticket: false },
{ name: 'Conductor', gender: "M", ticket: false },
{ name: 'Divya', gender: "F", ticket: true },
{ name: 'Kavya', gender: "F", ticket: true },
{ name: 'Sandya', gender: "F", ticket: true },
{ name: 'Vandya', gender: "F", ticket: true },
{ name: 'Hitesh', gender: "M", ticket: true },
{ name: 'Piyush', gender: "M", ticket: true },
{ name: 'Anirudh', gender: "M", ticket: false },
{ name: 'Jagdamba', gender: "M", ticket: true },
{ name: 'Dubey', gender: "M", ticket: true }
];

const arrFind = passengers.find(item => item.gender==="F");
console.log('arrFind ', arrFind ) 
// return the Divya details first F gender passenger

const arrSome = passengers.some(item => item.gender==="F"); 
console.log('arrSome ', arrSome )
// return TRUE bacause of some passengers gender are F

const arrEvery = passengers.every(item => item.gender==="F"); 
console.log('arrEvery ', arrEvery )
// return FALSE because not every passengers gender is F

const arrInclude = passengers.includes(item => item.gender==="F"); 
console.log('arrInclude ', arrInclude )
// return FALSE because not every passengers gender is F

const arrFilter = passengers.filter(item => item.ticket === false); 
console.log('arrFilter ', arrFilter )
// return list of ticket false list

.includes()

check for value incluedes

const names = ["Divya", "Kavya", "Hitesh"];
const arrInclude = names.includes("Divya");
console.log('arrInclude', arrInclude); //true

.map(), .flat() and .flatMap()

//.map(): used for any performance with each element
gents = ["Hitesh","Piyush","Jagdamba","Dubey"]
const isFriend = gents.map((f, i)=> f+" is my freind");
console.log(isFriend)
// ['Hitesh is my freind', 'Piyush is my freind', 'Jagdamba is my freind', 'Dubey is my freind']

//.flat(): used for combining multiple arrays into a single array
staff = ["dirver", "conductor"]
ladies = ["Divya","Kavya","Sita","Geeta"]
const newArr = [staff , ladies ].flat(); // merge arrays
console.log(newArr ); 
//(6) ['dirver', 'conductor', 'Divya', 'Kavya', 'Sita', 'Geeta']

// .flatMap compbined all values
const bus = [staff, ladies, gents].flatMap(p => p + ' in the bus'); 
console.log(bus);
//  ['dirver,conductor in the bus', 'Divya,Kavya,Sita,Geeta in the bus', 'Hitesh,Piyush,Jagdamba,Dubey in the bus']

.split() and .join()

let myFriends = "Hitesh,Piyush,Jagdamba,Dubey"
//.split(',') create array with diffence of given value
const friendArr = myFriends.split(',')
console.log(friendArr) //['Hitesh', 'Piyush', 'Jagdamba', 'Dubey']

// .join() create string from arrays
const names = frinedArr.join(',')
console.log(names) // 'Hitesh,Piyush,Jagdamba,Dubey'

.slice()

.slice() does not modified original array

let bus = ["Hitesh","Piyush","Jags","Students"]
const sliceBus = bus.slice(2)
console.log(bus) // ['Hitesh', 'Piyush', 'Jags', 'Students']
console.log(sliceBus)  // ['Jags', 'Students']

.splice()

.splice() update the original array and credendial

let bus = ["Hitesh","Piyush","Jags","Students"]
const sliceBus = bus.splice(2)
console.log(bus) // ['Hitesh', 'Piyush']
console.log(sliceBus)  // ['Jags', 'Students']

.reduce()

.reduce() is used for some calculations with all elements. like the total collection of bus tickets.

let ticketSold = [10,15,20,30,40,50,5];
let totalSold = ticketSold.reduce((total,perticket) => total + perticket,0); //returns 170

Surprise ... (create your own methods)

Array.prototype.ticketDone = function(mes){ 
let pList = []; 
for(let i = 0; i < this.length; i++){ 
    pList.push(mes(this[i])); 
} 
return pList; 
}

let bus = ["p1","p2","p3","p4","p5","p6","p7","p8"]
bus.ticketDone(pas => pas + " ticket kat gaya");
// ['p1 ticket kat gaya', 'p2 ticket kat gaya', 'p3 ticket kat gaya', 'p4 ticket kat gaya', 'p5 ticket kat gaya', 'p6 ticket kat gaya', 'p7 ticket kat gaya', 'p8 ticket kat gaya']

Summary

Now code summary is code try to better understand this.

const myArr = [1,2,3,4,5.5] myArr.length() 
// returns the array length ( count of items the array is 5)
myArr.at(n) 
// get the value of nth position ( 4th position value is 5.5)
myArr.indexOf(4) 
// get the position of value (5 is at 4th position)
myArr.concat(4,[45,56,76,86]) 
// add more value into the array (also can be single value or can be another array itself)
myArr.fill(0); 
// fill all the position with passed value
myArr.find((item) => item < 7) 
// check for the first item to match the condition
myArr.some((item) => item < 7) 
// check for the some item to match the condition
myArr.every((item) => item < 7) 
// check for all items to match the contions with iterations with true and false
myArr.includes(item); 
// return booleans if item avilable or not in the array
myArr.filter((item) => item >4) 
// return the list of the array with matched the conditions m
myArr.map(item => item * 2) 
// return the new array with any actions performed with each elements
myArr.flat(); 
// convert in the single array from multilevel array
myArr.flatMap(item => item + "a") 
// maping and also flat the array if there is multilevel array
myArr.join('-') 
// return string with all value differnciate with mentioned value
myArr.split('-') 
// return array with split value myArr.push(7) // add new item in the last of the array myArr.pop // removed and returns the last item of the array
myArr.unshift(0) 
// add new item or items in the start of array
myArr.shift() 
// removed first item from array
myArr.splice(start, count) 
// returns removed form old array and return the new array from start to number of counts
myArr.slice(count) 
// just slice removed or sliced from start to count
arr.reduce((total,item) => total+item,intial) 
// return the sum of the array with intial if added

collection of value with their labels can store in the variables

let person = {
  name: "JD",      // key: "name",  value: "Aryan"
  age:  36,          // key: "age",   value: 22
  city: "Noida",     // key: "city",  value: "Delhi"
  isStudent: true   // values can be any type
};

Access values/properties

2 ways of access value (dot and bracket notations)

let person = {
  name: "JD",      // key: "name",  value: "Aryan"
  age:  36,          // key: "age",   value: 22
  city: "Noida",     // key: "city",  value: "Delhi"
  isStudent: true   // values can be any type
};

// Access value through dot notations
console.log(person.name) // JD

// Access value through Bracket notations
console.log(person[age]) // 36

// both ways can access the any type of values

Updating Values

let person = {
  name: "JD",      // key: "name",  value: "Aryan"
  age:  36,          // key: "age",   value: 22
  city: "Noida",     // key: "city",  value: "Delhi"
  isStudent: true   // values can be any type
};

console.log(person.city) // Noida

person.city = "Delhi"

console.log(person.city) // Delhi

we can update values through both dot and bracket notations

Adding & Deleting Properties

let person = {
  name: "JD",      // key: "name",  value: "Aryan"
  age:  36,          // key: "age",   value: 22
  city: "Noida",     // key: "city",  value: "Delhi"
  isStudent: true   // values can be any type
};

person.email = "name@example.com"

console.log(person) 
//{name: 'JD', age: 36, city: 'Noida', isStudent: true, email: 'name@example.com'}

delete person.age
console.log(person) 
//{name: 'JD', city: 'Noida', isStudent: true, email: 'name@example.com'}

delete can help you to remove key and value

we can add values through both dot and bracket notations

Loop for Object

for... in loop can be used for object key and values like:

let person = {
  name: "JD",      // key: "name",  value: "Aryan"
  age:  36,          // key: "age",   value: 22
  city: "Noida",     // key: "city",  value: "Delhi"
  isStudent: true   // values can be any type
};

for (let key in person){
    console.log(key, " value is ", person[key])
}

// name  value is  JD
// age  value is  36
// city  value is  Noida
// isStudent  value is  true

Object vs Array

Summary

An object is a collection of related data and/or functionality. Unlike an array, which is an ordered list, an object is a structure where you give every piece of data a "label" (the key) so you can find it easily.

• Objects store related data together

• Use dot notation for simple access

• Use bracket notation for dynamic keys

• Use for...in to loop through properties

Simple variables

let friend1 = "Hitesh"
let friend2 = "Piyush"
let friend3 = "Anirudh"
let friend4 = "Jai"
let friend5 = "Jags"

But with Arrays

let friends = ["Hitesh","Piyush","Anirudh","Jai","Jags"]
// single group of collections of the list

Accessing Elements

with index we can acces the values like:

Index starts with 0

// index           0       1        2        3      4
let friends = ["Hitesh","Piyush","Anirudh","Jai","Jags"]

//print values (Access values)

console.log(friends[0]) // Hitesh
console.log(friends[2]) // Anirudh

Updating values

yes, we can update values from the list like:

let friends = ["Hitesh","Piyush","Anirudh","Jai","Jags"]

friends[2] = "Big Boss"

//now array will be
console.log(friends) 
// ['Hitesh', 'Piyush', 'Big Boss', 'Jai', 'Jags']

Array Length (count value of the arrays)

let friends = ["Hitesh","Piyush","Anirudh","Jai","Jags"]
// count the values of the arrays
console.log(friends.length) // 5

Looping Over Arrays

If you want do some action or any calculation use for of loop

let friends = ["Hitesh","Piyush","Anirudh","Jai","Jags"]
// count the values of the arrays
for (let friend of friends ) {
  console.log(friend + ' is my Friend');
}
// Hitesh is my Friend
// Piyush is my Friend
// Anirudh is my Friend
// Jai is my Friend
// Jags is my Friend

Summary

Array is the collection of values in a variable. it could be string, number, boolean all of the values can be

• we can create array with []

• Array can acccess with index like myArray[index]

• Array can be updated with index and assgin value like myArray[index] = newvalue

• Array can loop with for of loop

let movies = ["Movie1", "Movie2", "Movie3", "Movie4", "Movie5"];

console.log(movies[0]); // Movie1

movies[2] = "Movie2";

for (movie of movies) {
  console.log(movie);
}

Instead of writing the same code again and again, you wrap it inside a function and call it whenever needed.

like:

function add(a, b) {// syntax for creating function with vars 
  return a + b; // now code for adding 2 numbers
}
// now we call function with values which we need to perform action
console.log(add(2, 3)); // 5
// add is function and 2,3 are the values of 'a' and 'b' which functions required

as we see above this is function declaration,

Function Type

• function declartion

• function expression

//function declation as we already seen lets discuss both again
// Function Declaration
function add(a, b) {
  return a + b;
}

// Function Expression just same as above but it store in var
const addExp = function(a, b) {
  return a + b;
};

console.log(add(2, 3));     // 5 // calling way is the same 
console.log(addExp(2, 3));  // 5 // for function declation and expression

Hoisting

hosting is the issue when fuction call before creation.

• function declaration never create this issue

• function expression has the issue of hoisting because it store it the variable

console.log(multiply(2, 5)); // ✅ works

console.log(multiplyExp(2, 5)); // ❌ error

function multiply(a, b) {
  return a * b;
}

const multiplyExp = function(a, b) {
  return a * b;
};
// both works here
console.log(multiply(2, 5)); // ✅ works

console.log(multiplyExp(2, 5)); //✅ works

Hoisting means JavaScript moves declarations to the top

Summary

Functions is block of code which can process the different values which can be used in multple places which different values.

Use Function Declaration:

• When you want to define reusable functions early

• When you may call it before writing it

• simple, hoisted, beginner-friendly

Use Function Expression:

• When assigning functions to variables

• When using functions as values (common in modern JS)

• flexible, used more in modern JavaScript

Arithmetic Operations for Calculations

let a = 10;
let b = 3;

console.log(a + b); // 13 (addition)
console.log(a - b); // 7  (subtraction)
console.log(a * b); // 30 (multiplication)
console.log(a / b); // 3.33 (division)
console.log(a % b); // 1 (remainder)

Assignment Opertations

Used to assign or update values like:

let num = 10; // Assigining the values
// if we use  Arithmetic  then we can update assigned values
num += 5; // num = num + 5 → 15
num -= 3; // num = num - 3 → 12

Comparion Operations

this is intersting things let discuss

// like as earlier discussed
let a = 5 // single '='  is used for assign the value
let b = '5' // assigning number as string right?

// now '==' is used to compare the values
console.log(a == b) // true

// also '===' is used for compare value and its type
console.log(a ===b) // false because its number and string 

Let know some more things

let a = 5
let b = 10
// '<' '>' '!'
console.log(a > b) // false "is a is greater then b"
console.log(a < b) // true "is a is let then b"
console.log(a != b) // false "check for not eqal"
// ! is used for false or not.

Logical Opertaions

let go for more deeper for comparing values with combined coditions. Just Remember :

• && is used AND conditions

• || is used for OR condtions

• ! is used to check the not or falsy values

let age = 20;

console.log(age > 18 && age < 30); // true
console.log(age < 18 || age > 15); // true
console.log(!(age > 18)); // false
// go slow and revise it. there is 2 condtions which compared so 
//"&&" is used to check the both condtion is true and 
// "||" is used for to check at least 1 condition the true 
// "!" is checkign condition is false and it make opposite whatever condition is.

| A | B | A && B | A || B | ! for A | | --- | --- | --- | --- | --- | | true | true | true | true | false | | true | false | false | true | false | | false | true | false | true | true | | false | false | false | false | true |

Summary

JS is tools to play with data with some operators like

• Use + - * / % for math

• Use === instead of ==

• Use && and || for combining conditions

• Use +=, -= for cleaner updates

• AND (&&) → strict (needs both true)

• OR (||) → flexible (needs one true)

• NOT (!) → reverses result

Control Flow: The order in which code runs based on the conditions.
Instead of code run all line by line it has to ignore some lines through some coditions.

Use if conditions

let marks = 40

if(marks > 33){ // if with condtion of 33 value
    console.log('you are passed') // condtion true then run
}
// console.log (print) will only run if condtion match the values

Handle the other conditions

let marks = 40

if(marks > 33){ 
    console.log('you are passed')
} else {
    console.log('you are failed') //here is the others condition 
}
// In this code. console.log(print) statement will run. 

now we execute the condition with if and else one condition will run always

Lets add more conditions to discuss like

let marks = 40

if(marks > 33){ 
    console.log('you are passed')
if (marks > 90){ // add more condition with another values
    console.log('Got Grade A') 
if (marks > 75){ // add more condition with another values
    console.log('Got Grade B') 
} else {
    console.log('you are failed') 
}

runs code by checking conditions one by one and print the statement as per condition

Switch Statement

Used when you compare one value with many options

let day = 2;

switch (day) {            // difines variables 
  case 1:                 // case used for match the values 
    console.log("Monday");// if true then print 
    break;                // done and skip next (flow break)
  case 2:                     // previous not match 
    console.log("Tuesday");   // what need to be done
    break;                    // if match the end it
  case 3:
    console.log("Wednesday");
    break;
  case 4:
    console.log("Thursday");
    break;
  case 5:
    console.log("Friday");
    break;
  case 6:
    console.log("Saturday");
    break;
  case 7:
    console.log("Sunday");
    break; 
  default:                 // if none of condition matched 
    console.log("Invalid day");// run this code 
}

We can use Switch if we have multiple conditions with fixed values

When to use of if -else or switch

Summary

if we have conditions to run the code then Control flows comes in the pictures

• Use if → single condition

• Use if-else → two paths

• Use else if → multiple conditions

• Use switch → many fixed values

var name = "hello world";
// name is the container and hello World is the value/data

lets discuss about container, var is not the only way to assign the container, we have let and const which can also assign the container to store the values/data like:

var name = "hello world"; 
let age = 28;
const isStudent = true;

Key Differnces of var, let and const

Data/Values could be in multiple types...

Yes also we have multiple types of data. Primitive data types likes: text, number, truthy and so on...

let name = "hello JD" // 'String' for text or any other information
let age = 32 // 'number' can be data to be stored
let isWorking = true // 'boolean' is also data to be stored
let nothing = null // 'null' blank for now filled in the future
let notDefined = undefined // 'undefined' shows its not defined at

Basic for now for better understanding...

Scope

Scope is the area in where the can the access the container to get the values.
yes, we can control the container availability to be accessed

var gVar = "I am global" // called 'global scoped'
let gLet = "I am global" // can be accessed at everywhere
const gConst = "I am global"// till this file available

function outer(){ // just remember this bracket {function Scoped}
    var oVar = "I am outer (var)" // can be accessed
    let oLet = "I am outer (let)" // only inside the brackets
    const oConst = "I am outer (const)" // not accesble outside

    if(true){ // Again Brackets for area {block scoped}
        var bVar = "I am block (var)"
        let bLet = "I am block (let)"
        const bConst = "I am block (const)"
    }
}

Summary

As we understaind about In the web world every thing is data, so we use container (var,let,coist) to store. so the we have value at one place and use container name to avoid the rework at the time of value updation. Also we have some differences in between them (re-check table). And also we have multiple types of data/values to store basics for now. Scope (area of availabilty) for the container.

• use let if value updates

• use const if value is fixed

• var avoid using for future code.

.length

.length is used to get the total element count.

let bus = ["0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0"]
bus.length // 13 returns the array length ( count of items the array is 5)

.at() and .indexOf()

.at() and .indexOf are used to the passenger

let bus2 = ["driver","hitesh","piyush","anirudh","main bhi hu"]
bus2.at(3) // return anirudh it start from the 0 (doesn't include drive seat only passengers)
bus.indexOf("main bhi hu") // Return 4 position of the the value and starts with 0

.fill() and .concat()

.fill(1): Fill all the seats with 1 passenger
.concat(): add another bus passenger to your bus

bus3 = bus.fill(1) // update all values with 1
bus3 = bus2.concat(bus) //add new array with the old array

.push() and .pop()

add and remove items at ends of the array(list)
.push() // board new passenger from the back gate
.pop() // deboard passenger from the back gate

bus4 = bus.push('gents'); // gents boarded bus from back gate
bus4 = bus.pop('gents'); // after destination gents deboarded bus from back gate

.unshift() and .shift()

add and remove items at the start of the array(list)
.unshift() // boarded ladies passengers from front gate
.shift() // deboarded ladies passengers from front gate

.find(), .some(), .every(), .includes(), and .filter()

some other important methods of arrays
.find() // check for any lady passenger by name
.some() // check for any lady passenger by boolean
.every() // check for all passenger is women
.include() // any lady passenger by name
.filter() // give me the ladies passenger list

let ticketPrize = [5,7,10,15,20,30,40,60,80]
ticketPrize.find(item => item === 10) // return 10 the value if true
ticketPrize.some(item => item < 10) // return true beacuse of value 5 is lesser
ticketPrize.every(item => item < 10) // return false beacause of other value is higher
ticketPrize.includes(5) // return true because 5 is in the list
ticketPrize.filter(item => item <= 9) // [5, 7] retrun the value

const passengers = [
{ name: 'Driver', gender: "M", ticket: false },
{ name: 'Conductor', gender: "M", ticket: false },
{ name: 'Divya', gender: "F", ticket: true },
{ name: 'Kavya', gender: "F", ticket: true },
{ name: 'Sandya', gender: "F", ticket: true },
{ name: 'Vandya', gender: "F", ticket: true },
{ name: 'Hitesh', gender: "M", ticket: true },
{ name: 'Piyush', gender: "M", ticket: true },
{ name: 'Anirudh', gender: "M", ticket: false },
{ name: 'Jagdamba', gender: "M", ticket: true },
{ name: 'Dubey', gender: "M", ticket: true }
];

passengers.find(item => item.gender==="F"); // return the Divya details first F gender passenger
assengers.some(item => item.gender==="F"); // return TRUE bacause of some passengers gender are F
assengers.every(item => item.gender==="F"); // return FALSE because not every passengers gender is F
assengers.filter(item => item.ticket === false); return list of ticket false list

.map(), .flat() and .flatMap()

.map(): used for any performance with each element

ticketPrize = [5,7,10,15,20,30,40,60,80] dobledPrize = ticketPrize.map(prize => prize * 2) // new array with doubled prize

.flat(): used for combining multiple arrays into a single array
staff = ["dirver", "conductor"]
ladies = ["Divya","Kavya","Sita","Geeta"]
gents = ["Hitesh","Piyush","Jagdamba","Dubey"]
bus = [staff, ladies, gents].flat(); // get all value in one

bus = [staff, ladies, gents].flatMap(p => p + ' in the bus'); // get all value in one

.split() and .join()

.split() used for creating array
let myFriends = "Hitesh,Piyush,Jagdamba,Dubey"
frinedArr = myFriends.split(','); // create element on the based of ,
.join() is used for array to string
names = frinedArr.join(',') // array convert back to string

.slice() and .splice()

.slice()

this is used to slice the list bus Doesn't modify the original array and returns a new array with selected elements like: ticket done for some passenger some are pending but all are in the bus
let bus7 = ["driver","conductor","Hitesh","Piyush","Jags","Students"]
bus7.slice(2) // first 2 dirver and conductor does not require tickets
bus7.slice(2,5) // first 2 and after and after 5 (dirver and conductor and stundents and so not required)

.splice()

Modifies the original array and returns removed elements like: some of the passengers deboarded the bus but some still in the bus
let bus8 = ["driver","conductor","Hitesh","Piyush","Jags","Students"]
busSplice = bus8.splice(2) // store only passengers and bus8 has only dirver and conductor
busSplice = bus8.splice(2,3) // first value start from and second value count of delete/splice

.reduce()

reduce is used for some calculations with all elements. like the total collection of bus tickets.
let ticketSold = [10,15,20,30,40,50,5];
let totalSold = ticketSold.reduce((total,perticket) => total + perticket,0); //returns 170

Surprise Mee

surprise is that you can create your methods and surprise anyone which called polyfill lets create

I need to add the text "ticket kat gaya" for all bus passengers for tickets

Array.prototype.ticketDone = function(mes){ let pList = []; for(let i = 0; i < this.length; i++){ pList.push(mes(this[i])); } return pList; }

let bus = ["p1","p2","p3","p4","p5","p6","p7","p8"]
bus.ticketDone(pas => pas + " ticket kat gaya");

Conclusion + Revision

const myArr = [1,2,3,4,5.5] myArr.length() // returns the array length ( count of items the array is 5)
myArr.at(n) // get the value of nth position ( 4th position value is 5.5)
myArr.indexOf(4) // get the position of value (5 is at 4th position)
myArr.concat(4,[45,56,76,86]) // add more value into the array (also can be single value or can be another array itself)
myArr.fill(0); // fill all the position with passed value
myArr.find((item) => item < 7) // check for the first item to match the condition
myArr.some((item) => item < 7) // check for the some item to match the condition
myArr.every((item) => item < 7) // check for all items to match the contions with iterations with true and false
myArr.includes(item); // return booleans if item avilable or not in the array
myArr.filter((item) => item >4) // return the list of the array with matched the conditions m
myArr.map(item => item * 2) // return the new array with any actions performed with each elements
myArr.flat(); // convert in the single array from multilevel array
myArr.flatMap(item => item + "a") // maping and also flat the array if there is multilevel array
myArr.join('-') // return string with all value differnciate with mentioned value
myArr.split('-') // return array with split value myArr.push(7) // add new item in the last of the array myArr.pop // removed and returns the last item of the array
myArr.unshift(0) // add new item or items in the start of array
myArr.shift() // removed first item from array
myArr.splice(start, count) // returns removed form old array and return the new array from start to number of counts
myArr.slice(count) // just slice removed or sliced from start to count
arr.reduce((total,item) => total+item,intial) // return the sum of the array with intial if added

Polyfill to create your custom methods

Array.prototype.myMap = function(fn){
myArr = []
for(let i=0; i<this.length; i++){
myArr.push(fn(this[i]))
}
return myArr;
}