Functional programming can be defined as a style of programming paradigm in which we try to combine everything in pure mathematical functions. Basically, it is a declarative type of paradigm style. It is unique as compared to other programming paradigms as it is based on mathematical functions.

Furthermore, its main focus is “what to solve” and, in contrast to an imperative style where the main focus is “how to solve”. Moreover, these programming languages are specifically designed to handle symbolic computations and list processing applications. Also, some of the popular functional programming languages include: Lisp, Python, Erlang, Haskell, Clojure, etc.

CHARACTERISTICS –

Some of the most important and specific characteristics of functional programming are as follows :

• Functional programming languages are specifically created and designed purely on the concept of mathematical functions that use conditional expressions and recursion to perform a computation.
• Most noteworthy, Functional programming languages don’t support flow Controls like loop statements such as WHILE, FOR. And conditional statements like IF-ELSE and SWITCH Statements. They directly use the functions and functional calls.
•  Functional programming also supports higher-order functions and lazy evaluation features all along.
•  Like Object-oriented Programming, functional programming languages also support popular concepts such as Abstraction, Encapsulation, Inheritance, and Polymorphism.

ADVANTAGES –

Functional programming provides the following advantages:

•  Functional programming does not support state, so there are no side-effect results and we can write error-free codes. Thus, no BUGS in the code. BUGS-FREE CODE .
• Functional programming is more efficient as it consists of independent units that can run concurrently. 
• These programming languages have NO Mutable state. Thus, there are no state-change issues. One can program "Functions" so as to work parallel as "instructions". Such codes support easy reusability and testability.

As a down point, functional programming requires a large memory space. The main reason is that it does not have state, you need to create new objects each and every time to perform actions.

More specifically, Functional Programming is applied in situations where we need to perform numerous of different operations on homogenous set of data.

CATEGORISATION –

Functional programming languages can be categorized into two groups that are stated below –

• Pure Functional Programming Languages − These types of functional programming languages support only the functional paradigms. For example − Haskell.
•  Impure Functional Programming Languages − These types of functional programming languages support the functional paradigms and imperative style programming. For example − LISP.

Most relevantly, an efficient functional programming code can reduce resource consumption and completion time as much as possible with minimum risk to the operating environment.

IMPORTANT CONCEPTS AND TERMINOLOGIES –

Before one becomes an expert in functional programming, there are some important and specific concepts that one needs to understand :

•         Pure functions

•         Function composition

•         Shared states

•         Recursion

•         Referential transparency

•         Functions are First-Class and can be Higher-Order

•         Variables are Immutable

CONCLUSION –

Working in the web development industry surely requires adaptability. The more we know, the more opportunities we'll have for advancing and strengthening our career. If you won’t keep expanding your set of skills, you could find yourself unable to compete in the job market full of competition.

If you’re looking for a way to write code more specifically, concisely, concurrently and even want to improve the performance of your code in an efficient way, learning how to use functional programming will be beneficial definitely.