/**Function declaration vs Expression */

function walk(){

console.log('walk');

}

/**Named Function */

let x = function run(){

console.log('run');

};

/**Anonymous Function */

let run = function(){

console.log('run');

};

walk();run();x();

/**Hoisting: Moving function declaration to the top of the file automatically by javascript

* (not work in case of function expression)

* */

a();

function a(){

console.log('a');

}

/**Arguments */

function sum(a, b){

console.log(arguments);

return a+b;

}

function add(){

console.log(arguments);

let total = 0;

for(let value of arguments) total+=value;

return total;

}

console.log(sum());//undefined +undefined = NaN

console.log(sum(1));//1 +undefined = NaN

console.log(sum(1,2))

console.log(add(1,2,3,4,5))

/**The Rest operator (not spread operator: Don't confuse)

* The Rest operator parameter should be the last parameter(Rest of the parameters) in method always else error

*/

function add1(...args){

return args.reduce((a,b)=>a+b);

}

console.log(add1(1,2,3,4,5))

function sum1(discount, ...prices){

total = prices.reduce((a,c)=>a+c);

return total * (1-discount);

}

console.log(sum1(0.1, 20,30));

/**Default Parameters */

function add3(x=3,y,z=5){

return x+y+z;

}

console.log(add3(20,30));

console.log(add3(undefined,20,30));

console.log(add3(10,20,undefined));

console.log(add3(10));

/**Getter and Setters */

const employee = {

firstName:'Sumit',

lastName:'Kumar',

get fullName(){

return `${employee.firstName} ${employee.lastName}`;

},

set fullName(value){

/**Exception handling with try catch and throw exception */

if(typeof value !=='string') throw new Error('Value is not a String');

const parts = value.split(' ');

if(parts.length !== 2) throw new Error('Enter a first and a last name');

employee.firstName = parts[0];

employee.lastName = parts[1];

}

}

employee.fullName = 'Anil Kumar';

/**Try and catch */

try{

employee.fullName = 'Ram chandra bhansal';

}catch(e){

console.log(e.message);

}

console.log(employee.fullName);

/**Local vs Global Scope */

const message = 'Hi';

console.log(message);

//blocked scope

{

const message1 = 'Hello';

}

///console.log(message1); //ReferenceError: message1 is not defined

//local variable take precedence over global variable

const message2 = 'I am Global variable';

function a1(){

console.log(message2);

}

function a2(){

console.log(message2);

}

function a3(){

const message2 = 'I am Local variable'

console.log(message2);

}

a1();

a2();

a3();

/**let vs var

* let and const: create block scope variable (ES2015:ES6)

* var: create function scope variable

*/

function letstart(){

for(let i=0; i<5; i++){

console.log(i);

}

// console.log(i); // In case of let://ReferenceError: i is not defined

}

function varstart(){

for(var i=0; i<5; i++){

console.log(i);

}

console.log(i); // In case of var it will run without issue

}

// console.log(i); //Due to function scope:// In case of let or var://ReferenceError: i is not defined

{

var m = 'access';

}

console.log(m); // allowed due to block scope

letstart();

varstart();

/**this keyword : see output to understand which one returns what*/

const video ={

title:'a',

tags:['a', 'b', 'c'],

showTags(){

this.tags.forEach(function(tag){

console.log(this, tag); // here this is global object: it print 3 times global object

});

},

showTags2(){

this.tags.forEach(function(tag){

console.log(this, tag); // here this is current object: it print 3 times current object

}, this); // because of second argument to for each loop which takes an object

},

play(){

console.log(this);

}

};

video.play();

video.showTags();

video.showTags2();

function playVideo(){

console.log(this);

}

playVideo();

function Video(title){

this.title = title;

console.log(this);

}

const v = new Video('a');

console.log(this);

video.showTags();

video.showTags2();

/**Changing this: Solution 1: not a prefered approach but why ? */

const video1 = {

title:'a',

tags: ['a', 'b', 'c'],

showTags(){

const that = this;

this.tags.forEach(function(tag){

console.log(that.title,tag);

});

}

};

video1.showTags();

/**Changing this: Solution 2 : using call, apply, bind functions*/

function playVideo5(a, b){

console.log(this);

}

playVideo5();//call global oject

playVideo5.call({name:'sumit'}, 1,2);//call specified oject in first argument of call with comma sepereated argument

playVideo5.apply({name:'sumit'},[1,2]);//call specified oject in first argument of call with array based argument

playVideo5.bind({name:'sumit'})();

const video2 = {

title:'a',

tags: ['a', 'b', 'c'],

showTags(){

this.tags.forEach(function(tag){

console.log(this.title,tag);

}.bind(this));

}

};

video2.showTags();

/**Changing this: Solution 3 : using arrow function from ECMA2015 ES6*/

const video3 = {

title:'a',

tags: ['a', 'b', 'c'],

showTags(){

this.tags.forEach(tag=>

console.log(this.title,tag) /// arrow function will inherit this object from the top

);

}

};

video3.showTags();