Currying function is a popular technique in functional programming, and it’s an essential concept to master when writing JavaScript code. Currying function is a way to transform a function with multiple arguments into a sequence of functions that each take a single argument. In other words, currying converts a function of N arguments into a chain of N functions that each take one argument.

Currying is useful in many situations where you need to create specialized versions of a function. For example, suppose you have a function that adds two numbers together:

```
function add(a, b) {
return a + b;
}
```

Now, imagine that you want to create a specialized version of the `add`

function that always adds a certain number to the input value. You could achieve this with currying:

```
function addN(n) {
return function(m) {
return n + m;
}
}
const add3 = addN(3);
console.log(add3(7)); // Output: 10
```

In this example, `addN`

is a curried version of `add`

. It returns a new function that takes a single argument `m`

and returns the sum of `n`

and `m`

. When you call `addN(3)`

, you get a new function that always adds `3`

to its input value.

Another advantage of currying is that it can simplify the process of creating partial functions. A partial function is a function that is pre-configured with some of its arguments. For example, suppose you have a function that takes three arguments:

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

Now, imagine that you want to create a specialized version of the `multiply`

function that always multiplies the first two arguments by a certain number. You could use currying to create a partial function like this:

```
function multiplyPartial(n) {
return function(a, b) {
return multiply(n, a, b);
}
}
const multiplyBy5 = multiplyPartial(5);
console.log(multiplyBy5(2, 3)); // Output: 30
```

In this example, `multiplyPartial`

is a curried version of `multiply`

. It returns a new function that takes two arguments `a`

and `b`

, and calls `multiply`

with the pre-configured value `n`

and the two input arguments. When you call `multiplyPartial(5)`

, you get a new function that always multiplies its first two arguments by `5`

.

In JavaScript, you can use the `bind`

method to create a curried version of a function. For example, you can rewrite the `addN`

function like this:

```
function addN(n) {
return function(m) {
return n + m;
}
}
const add3 = addN.bind(null, 3);
console.log(add3(7)); // Output: 10
```

In this example, `addN.bind(null, 3)`

creates a new function that takes a single argument `m`

, and calls `addN`

with the pre-configured value `3`

and the input argument `m`

. The first argument to `bind`

is the value of `this`

inside the function, which is not used in this case.

Currying is a powerful technique that can help you write more concise and reusable code. By breaking down a function with multiple arguments into a series of functions with single arguments, you can create specialized and partial functions that are easier to understand and maintain.