Function Composition

Function composition is a technique where you combine two or more functions to produce a new function. The output of one function becomes the input of the next. This leads to cleaner, reusable, and readable code.

How Function Composition Works

• Call the innermost function first.
• Pass its result to the next function.
• Continue until all functions execute.
• Return the final output.

const double = x => x * 2;
const increment = x => x + 1;

// Compose functions manually
const incrementThenDouble = x => double(increment(x));

console.log(incrementThenDouble(3)); // Output: 8
// Explanation: increment(3) => 4, then double(4) => 8

Here, incrementThenDouble is a composed function that combines two operations in sequence.

Utility: Writing a Compose Function

To generalize composition, you can write a helper function that composes multiple functions:

const compose = (f, g) => x => f(g(x));

const double = x => x * 2;
const increment = x => x + 1;

const incrementThenDouble = compose(double, increment);

console.log(incrementThenDouble(5)); // Output: 12
// increment(5) => 6, double(6) => 12

Benefits of Using Function Composition

• Modularity: Build complex logic from simple functions.
• Readability: Clear flow of data transformations.
• Reusability: Functions stay pure and focused.

Summary

• Function composition chains functions so output flows through each.
• Compose manually or with helper functions.
• Order of functions affects the result.