Javascript

 //single line comment


/* multi

line

comment*/


// let, const


//string, numbers, boolean, null, undefined

const name = 'hemanth';

const age = 28;

const rating = 4.5;

const isCool = true;

const x = null;

const y = undefined;

let z;


console.log(typeof name);





//strings

const name = 'hemanth';

const age = 28;


//concatination

console.log('my name is '+name+  ' and I am '+ age);


//template string

console.log(`my name is ${name} and I am ${age}`);


const hello = `my name is ${name} and I am ${age}`;


console.log(hello);


//string functions


const s ='hello world';


console.log(s.length);

console.log(s.toUpperCase());

console.log(s.toLowerCase());

console.log(s.substring(0, 5));

console.log(s.substring(0,5).toUpperCase());

console.log(s.split(''));


const t = 'technology, computers, it, code';

console.log(t.split(', '));




//arrays


/* array using constructor, new keyword and 

something after that means it is called constructor */


const numbers = new Array(1,2,3,4,5);

console.log(numbers);


//we can give multiple types in single array in js


const fruits = ['apples', 'oranges', 'pears', 10, true];


const fruits = ['apples', 'oranges', 'pears'];


console.log(fruits);

console.log(fruits[1]);


fruits[3] = 'grapes';

console.log(fruits);


fruits.push('mangos'); //add item to last

fruits.unshift('strawberries');//add item to front

fruits.pop();//last one off


console.log(Array.isArray(fruits));


console.log(fruits.indexOf('oranges'));




//object literals


const person = {

    firstName: 'hemanth',

    lastName: 'kumar',

    age: 28,

    hobbies: ['music', 'movies', 'sports'],

    address: {

        street: '50 main st',

        city: 'boston',

        state: 'ma'

    }

}


console.log(person);

console.log(person.firstName);

console.log(person.firstName, person.lastName);

console.log(person.hobbies[1]);

console.log(person.address.city);


//structuring

const {firstName, lastName, address:{city}} = person;

console.log(firstName);

console.log(city);


person.email='hemanth@mail.com';

console.log(person);





//array of objects


const todos = [

    {

        id:1,

        text:'take out trash',

        isCompleted:true

    },

    {

        id:2,

        text:'meeting with boss',

        isCompleted:true

    },

    {

        id:3,

        text:'dentist appt',

        isCompleted:false

    },

];


console.log(todos);

console.log(todos[1].text)


const todoJSON = JSON.stringify(todos);

console.log(todoJSON);






//for

for(let i=0;i<=10;i++) {

    console.log(i);

}


for(let i=0;i<=10;i++) {

    console.log(`for loop number: ${i}`);

}



//while

let i=0;

while(i<10) {

    console.log(i);

    i++;

}


//do while


let i = 1;


do {

  console.log(i);

  i++;

} while (i <= 10);



//break


for (let i = 1; i <= 10; i++) {

  if (i === 5) {

    break; // exits the loop

  }

  console.log(i);

}



//continue


for (let i = 1; i <= 10; i++) {

  if (i === 5) {

    continue; // skip when i is 5

  }

  console.log(i);

}




const todos = [

    {

        id:1,

        text:'take out trash',

        isCompleted:true

    },

    {

        id:2,

        text:'meeting with boss',

        isCompleted:true

    },

    {

        id:3,

        text:'dentist appt',

        isCompleted:false

    },

];



for (let i=0;i<todos.length;i++) {

    console.log(todos[i].text);

}



for (let todo of todos) {

    console.log (todo.text);

}


//for of


const numbers = [10, 20, 30];


for (const num of numbers) {

  console.log(num);

}




//foreach, map, filter

todos.forEach(function(todo) {

    console.log(todo.text);

});


const todoText = todos.map(function(todo) {

    return todo.text;

});

console.log(todoText);


const todoCompleted = todos.filter(function(todo) {

    return todo.isCompleted === true;

});

console.log(todoCompleted);


const todoCompleted = todos.filter(function(todo) {

    return todo.isCompleted === true;

}).map(function(todo) {

    return todo.text;

})

console.log(todoCompleted);





//foreach with syntax

array.forEach(function(currentValue, index, array) {

    // code to execute for each element

});


let numbers = [10, 20, 30, 40];


numbers.forEach(function(num) {

    console.log(num);

});


//map with syntax

let newArray = oldArray.map(function(element, index, array) {

    // return something for newArray

});


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


// Using map to double each number

let doubled = numbers.map(function(num) {

    return num * 2;

});


console.log("Original array:", numbers);

console.log("Doubled array:", doubled);



//filter with syntax

let newArray = oldArray.filter(function(element, index, array) {

    // return true to keep element, false to skip it

});


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


// Using filter to select even numbers

let evenNumbers = numbers.filter(function(num) {

    return num % 2 === 0;

});


console.log("Original array:", numbers);

console.log("Even numbers:", evenNumbers);



1. forEach():- Runs a function for every element in an array.

const numbers = [1, 2, 3, 4];


numbers.forEach(function(num) {

    console.log(num * 2);

});


Output:-

2

4

6

8


2. map():- Creates a new array by transforming each element.

const numbers = [1, 2, 3, 4];


const doubled = numbers.map(function(num) {

    return num * 2;

});


console.log(doubled);


Output:-

[2, 4, 6, 8]


3. filter():- Creates a new array with elements that pass a condition.

const numbers = [1, 2, 3, 4];


const evenNumbers = numbers.filter(function(num) {

    return num % 2 === 0;

});


console.log(evenNumbers);


Output:-

[2, 4]









const x = 10;


if(x===10) {

    console.log('x is 10');

} else if(x>10) {

    console.log('x is greater than 10');

}else  {

    console.log('x is less than 10');

}


const x = 10;

const y = 11;


if(x>5||y>10) {

    console.log('x is more than 5 or y is more than 10');

}



const x = 11;

const color = x>10?'red': 'blue';

console.log(color);





const color = 'green';


switch (color) {

    case 'red':

        console.log('color is red');

        break;

    case 'blue':

        console.log('color is blue');

        break;

    default:

        console.log('color is not red or blue');

        break;

}




//function

function addNums(num1 =1, num2 = 1) {

    return num1 + num2;

}


console.log(addNums(5,5));


//arrow function

const addNums=(num1 =1, num2 = 1)=> {

    return num1 + num2;

}

console.log(addNums(5,5));



const addNums=(num1 =1, num2=1)=>{

    console.log(num1+num2);

}

addNums(5, 5);


const addNums=(num1 =1, num2=1)=> console.log(num1+num2);

addNums(5, 5);



const addNums=(num1 =1, num2=1)=> num1+num2;

console.log(addNums(5, 5));


const addNums=num1=>num1+5;

console.log(addNums(5));





//constructor ex 1

function Person() {

    this.name="unknown";

    this.age=0;

}

const person1=new Person();

console.log(person1.name);

console.log(person1.age);


//constructor ex 2

function Person(name, age) {

    this.name = name;

    this.age = age;

}

const person1= new Person("hemanth", 28);

const person2= new Person("unknown", 30);


console.log(person1.name, person1.age);

console.log(person2.name, person2.age);


//constructor ex 3 adding methods inside constructor

function Person(name, age) {

    this.name = name;

    this.age = age;

    this.greet=function() {

        return `hello I am ${this.name}`;

    };

}

const person= new Person("hemanth", 28);

console.log(person.greet());




//constructor ex 4 using prototype

function Person(name, age) {

    this.name = name;

    this.age = age;

}


Person.prototype.greet=function() {

    return `hello I am ${this.name}`;

};


const person1= new Person("hemanth", 28);

console.log(person1.greet());

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