JavaScript: Higher-Order Functions (In-Depth)

A higher-order function is a function that either receives another function as an argument, returns a function, or both. They are foundational in JavaScript's functional programming style.

What is a Higher-Order Function?

Takes one or more functions as arguments (callbacks)
Returns a new function
Enables composition, abstraction, and code reuse

Example: Passing Functions as Arguments

function repeat(n, action) {
  for (let i = 0; i < n; i++) {
    action(i);
  }
}
repeat(3, console.log);

// Output:
0
1
2

Example: Returning Functions

function multiplier(x) {
  return function(y) {
    return x * y;
  }
}
const double = multiplier(2);
double(5); // 10

// Output:
10

Common Built-In Higher-Order Functions

map - Array transformation
filter - Select items from an array
reduce - Accumulate values in an array
forEach - Execute a function for each array item
setTimeout, setInterval - Delay or repeat actions

Why Use Higher-Order Functions?

Encourage code reuse and abstraction
Enable functional programming paradigms
Promote composability and cleaner code

Practice: Try writing a custom filter or map higher-order function to solidify your understanding!