Everything about Currying in JavaScript

Explanation of Function Currying in Javascript

Currying is generally a process in functional programming which helps to transform a function with multiple arguments into a series of nesting functions. It is also known as an advanced technique of working with functions in javascript.

Currying is not only used in javascript but in other languages as well. In simple words, we can say that currying is just a transformation of functions that translate a function from a callable as f(1,2,3) as f(1)(2)(3).

Importance of Currying
  • Currying generally helps us to avoid passing the same variable multiple times.
  • It also helps us to create a high order function

In this article, we will be covering function currying. We will generally learn two ways to curry our functions the first one is to use bind functions and the second one by using the concepts of closures.

Function Currying using the bind method 

To understand function currying by using the bind method let us create a function multiply. This function basically multiplies two parameters x and y and logs it to the console.

Now let us create another function multiplyByTwo which is exactly the copy of multiply. We will generally create this copy by executing the bind method over multiply. Over here we will pass generally passing some arguments. The second argument we will pass is 2.

As we know that when we call the bind method gives the copy of the multiply method and doesn’t invoke it directly. So this means that the value 2 will be set as the value of x. So now let us execute the multiplyByTwo function. Similarly, we can create a multiplyByThree function also and applying function currying.

Example 1.

Currying in Javascript Example


Currying in Javascript Output

Seeing the above example it is clear that the output will be 10 and 15. The reason for this is in multiplyByTwo function we are passing 2 as the first value and using the bind function on multiply so this is being passed to x and x becomes 2 and during the invocation of multiplyByTwo function we are passing 5 so this is being passed to y and y becomes 5. So the output becomes 10.

Similarly, the same thing happens for multiplyByThree function so the output becomes 15 as we are passing 3 as the first value. So this what currying is we can use multiply method to create multiplyByTwo and

So let us take a scenario where we pass more parameters to multiplyByTwo and multiplyByThree function. Let us now check what the output will be for this scenario.

Example 2:

Currying in Javascript Scenario

In the above example, the value 3 passed to multiplyByTwo function will end up being y over the multiply function. So it will generally ignore 5 which we pass on the multiplyByTwo function. So the result on the invocation multiplyByTwo will be 6. Similarly, the value which is 4 in this case passed to the multiplyByThree function will end up being the value of y over the multiply function so the output will be 12 on the invocation of multiplyByThree function. This is the beauty of function currying in javascript.


Currying in Javascript Output

Function Currying using closures in Javascript

As we discussed above that there are two ways to implement function currying in javascript. So now we will talk about how to implement function currying by using closures.

Let us understand it with the help of an example


currying in javascript using closures

In the above example, we have created a function multiply which returns another function and inside that function, we log the multiplication of x and y. In the multiply function when a new function is returned as is mentioned above. So the function has access to the x variable after it is returned. So it is something like creating a box in which x and this function exist. So this x will be preset to the specific value which can be accessed in the console.

Now let us create another function multiplyByTwo and in this function instead of bind, we will directly pass 2 as an argument to the multiply method. And while invoking the function  multiplyByTwo we will pass 3 as an argument. So, the output will be 6 when we invoke the multiplyByTwo function. Similarly the same thing will happen for multiplyByThree function and as we have passed 2 to multiply method and 5 during invocation of the multiplyByThree function the output will be 10.

This is a simple example of implementing currying using closures in javascript.


currying in javascript using closures output

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