I am sure we all know what currying is, in JavaScript. If not don't worry I have got you covered here.

A lot of people know the theory of currying, but not a lot of them, can implement the same. Implementing currying is extremely simple!

So what is currying?

Currying is a technique of evaluating function with multiple arguments, into a sequence of functions having lesser number of arguments.

Let's say a function can take in 3 arguments, we can curry this function, into a sequence of 3 functions taking 1 argument each, or into 2 functions taking 2 and 1 arguments each. So basically when we curry a function, we reduce the number of arguments it takes in, but still performs all the actions it was intended to.

I am sure you will understand this better with this piece of code.

//Function 1
const sum  = function (a) {
    return function (b) {
      if (b) {
        return sum(a+b);
      }
      return a;
    }
};
//Function 2
function num_sum(a, b){
   return a+b;
}
num_sum(1,2);
sum(1)(2)(3)..(n);

Function 2 is a traditional way of adding 2 numbers. Function 1 is the curried version of the same function where, we have reduced the number of arguments it has, in each function. Currying uses many concepts like high-order functions, where we can return a function or assign it to a value or even pass it as an argument to another function!

Let me show you another variant of currying the same sum function:

function sum(a,b){  
 return a + b;
}

function curry(f){
   return function(a){
       return function(b){
           return f(a,b);
       }
   }
}

let curriedSum = curry(sum);

let ans = curriedSum(1)(2);

In this example, we are currying an already existing function. Basically, by doing this we can re-use it with various number of arguments at different parts of a program depending on our needs.

Advantages of Currying:
1) Currying helps you to avoid passing the same variable again and again.
2) It helps to create a higher order function. It extremely helpful in event handling.
3) Little snippets of code can be written and reused with ease.