Callbacks and Higher-Order Functions

What does the following code demonstrate?

function multiplier(factor) {
  return function(number) {
    return number * factor;
  };
}

const double = multiplier(2);
const triple = multiplier(3);

console.log(double(5)); // 10
console.log(triple(5)); // 15

Callback hell
Function currying
A simple higher-order function with closure
This code demonstrates a simple higher-order function with closure. The multiplier function returns a new function that remembers the factor value through closure. When we call multiplier(2), it returns a function that will multiply any input by 2, which we assign to double. Similarly, triple will multiply any input by 3. This pattern allows us to create specialized functions from a more general one. While this has similarities to currying (partial application of arguments), true currying would transform a function taking multiple arguments into a sequence of single-argument functions.
Recursion

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