• In JavaScript, all functions are object methods.

• If a function is not a method of a JavaScript object, it is a function of the global object.

• We can discuss some methods here and will try to understand them properly with the help of practical examples.

const AirIndia = {
airline: "Tata",
iataCode: "TH",
bookings : [],
book( flightNum , name){
console.log(
`${name} booked a seat on ${this.airline} flight ${this.iataCode} ${flightNum}`
);
this.bookings.push({flight : `${this.iataCode} ${flightNum}` , name });
},
};

AirIndia.book(239 , "Jayesh Hande" );    // Jayesh Hande booked a seat on AirIndia flight TH239

AirIndia.book(723 , "Kunal Mirgal" );     // Kunal Mirgal booked a seat on AirIndia flight TH239

console.log(AirIndia);

• Now we will create a copy of the AirIndia function and store it in another variable book which also works as a function.

const book  =  AirIndia.book;

• but we can't access the book function from the AirIndia object and it gives a TypeError.
• because it works as a regular function call and this keyword from the AirIndia object is not accessible.
• Hence this keyword depends on how the function is called.
• Well, basically we need to tell JavaScript explicitly what's the dispute here should be like so if we want to book a lot of the flights.

const eurowings  = {
airline: "Eurowings",
iataCode : "EW" ,
bookings : [] ,
};

1) Call() method

 book.call(eurowings , 22 , "Jayesh Hande" );
 console.log( eurowings );

book.call(AirIndia , 33 , "Kunal Mirgal" );
console.log( AirIndia )

• By using the call () method we tell the function who calls the function by just passing the object as an argument along with the other parameters.
• It helps to avoid writing unnecessary duplicate code and also we can call declared functions by different objects.
• we are also able to use the this keyword in objects by normal function

2) Apply() method

• It does not receive a list of arguments instead it takes an array of arguments.

const flightData = [33 , "Kunal Mirgal"];

book.apply(eurowings , flightData);
console.log(eurowings);

• but now there is a better way to pass an array rather than using apply method. By using spread operator

book.call(eurowings , ...flightData)
console.log(eurowings);

• It works the same as apply() method.

3) Bind() method

• Bind() method is one of the most important methods in JavaScript.
• We can use the bind method to create a new function with the this keyword.

const bookEW  = book.bind(eurowings);

bookEW (27, "Akshad Jaiswal")

• This will not be called the book function. Instead, it will return a new function
• This now looks like the normal book function call again, and that's because in this function you already have the this keyword set in stone, basically.
• So, we no longer need to specify the this keyword again. That's the beauty of the bind() function.
• bind() method is an important and long topic. so I put a link to mdn docs here so that you can get more detailed knowledge about it. link: "developer.mozilla.org/en-US/docs/Web/JavaSc.."

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