# Function Methods in JavaScript.

- 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: "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind"


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