Question

How to use higher-order functions in JavaScript

Answer 1

// A higher‑order function is a function that does at least one of the following:
// 1. Takes another function as an argument
// 2. Returns a function as its result
// If it does either one, it qualifies.

// Higher-order function: takes a function as an argument
function applyTwice(fn, x) {
    return fn(fn(x));
}

// A simple function to pass in
function add3(n) {
    return n + 3;
}

// Use the higher-order function
const result = applyTwice(add3, 5); // 5 + 3 = 8 + 3 = 11

console.log(result);



/*
run:

11

*/

 

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Answer 2

// A higher‑order function is a function that does at least one of the following:
// 1. Takes another function as an argument
// 2. Returns a function as its result
// If it does either one, it qualifies.
 
// makeMultiplier is a higher‑order function because it RETURNS another function
function makeMultiplier(n) {
 
    // This inner function forms a closure and remembers the value of n
    return function(x) {
        return x * n; // Uses the captured value n
    };
}
 
// double_val is now a function created by makeMultiplier(2)
// It remembers n = 2 through closure
const double_val = makeMultiplier(2);
 
// Calling double_val(10) multiplies 10 by the captured n (which is 2)
console.log(double_val(10));
 
 
/*
run:
 
20
 
*/

 

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