Functional Programming Concepts
Functional Programming (FP) is a programming paradigm where programs are constructed by applying and composing functions. It is a declarative programming paradigm in which function definitions are trees of expressions that map values to other values, rather than a sequence of imperative statements which update the running state of the program.
1. First-Class Functions
In JavaScript, functions are treated as first-class citizens. This means functions can be:
- Assigned to variables.
- Passed as arguments to other functions.
- Returned from other functions.
const sayHello = function() {
return "Hello!";
};2. Pure Functions
A pure function is a function where the return value is determined only by its input values, without observable side effects.
- Deterministic: Given the same input, it will always return the same output.
- No Side Effects: It doesn't modify external state (variables, DOM, console, etc.).
// Pure
function add(a, b) {
return a + b;
};
// Impure (relies on external state)
let z = 10;
function addZ(x) {
return x + z;
};3. Immutability
Immutability means that once a data structure is created, it cannot be changed. Instead of modifying existing objects, you create new ones with the updated values.
const person = { name: "John", age: 25 };
// Bad (Mutation)
person.age = 26;
// Good (Immutability)
const updatedPerson = { ...person, age: 26 };4. Higher-Order Functions
A higher-order function is a function that takes one or more functions as arguments, or returns a function as its result. map, filter, and reduce are classic examples.
const numbers = [1, 2, 3];
const doubled = numbers.map(n => n * 2); // map takes a function5. Function Composition
Function composition is the process of combining two or more functions to produce a new function. Composing functions f and g produces f(g(x)).
programming/javascript/vanilla/javascript programming/javascript/vanilla/map-filter-reduce programming/javascript/vanilla/currying