The **`bind()` function** in JavaScript is used to make a function more specific in its usage. There are two types of '***binding***':

<br>

# 1. Binding an object

A function declared in a class can be called through *any* instance of that class; but, what if we want a function which can perform ***only*** the task of *one* instance of that class and can be called without using that instance? For this scenario, instead of writing a new function from scratch, we use the `bind()` method to create a modified copy of that function. The **first argument** for the `bind()` method is necessary, and it is the object with which we want to bind our new copy of the function. The keyword `this`, everywhere in the copy, will now refer to this ***bound*** object.

## Example

Suppose there is a class, `Person`, with the method `printName()`. To print information for "Katy", without writing a completely new function, we require a function `printKaty()`. Now, we are able to pass the object `Katy` (type: `Person`) to the `bind()` method which will **return** our required function:

class Person{
  constructor(name, age){
    this.name = name;
    this.age = age;
  }
}

Person.prototype.printName = function(){
  console.log(this.name + ' ' + this.age);
}

var katy = new Person("Katy", 25);

var printKaty = Person.prototype.printName.bind(katy);
printKaty();

# 2. Binding a parameter

If there is need to specify the arguments passed to a function, we can pass those fixed values in `bind()` after the first argument. Now, this new function will be called by passing the **unbound arguments** normally; these unbound arguments will first be **appended** to the bound arguments, and then the original function will be called.

## Example

Let us say `multiply(a, b)` multiplies two numbers. We can '***bind***' parameter `a` to 2 so that it always returns `b` multiplied by 2. This gives us a new function, `double(x)`, without having to write it.

> **Note:** Pass `this` as the first argument when binding a function which is NOT part of a class.

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

var double = multiply.bind(this, 2);
console.log(double(3));

What is the JavaScript bind?

The bind() function in JavaScript is used to make a function more specific in its usage. There are two types of  binding :  1. Binding an object A function declared in a class can be called through any instance of that class; but, what if we want a function which can perform only the task of one instance of that class and can be called without using that instance? For this scenario, instead of writing a new function from scratch, we use the bind() method to create a modified copy of that function. The first argument for the bind() method is necessary, and it is the object with which we want to bind our new copy of the function. The keyword this, everywhere in the copy, will now refer to this bound object. Example Suppose there is a class, Person, with the method printName(). To print information for “Katy”, without writing a completely new function, we require a function printKaty(). Now, we are able to pass the object Katy (type: Person) to the bind() method which will return our required function: 