Higher-Order Functions

Question 1

What kind of function gets passed as an argument to another function?

Answer 1

Callback function

Question 2

What kind of function accepts other functions as arguments?

Answer 2

Higher-order function

Question 3

Operations started only after preceding ones have completed are

Answer 3

Synchronous

Question 4

4 ways functions are data

Answer 4

Pass them to other functions
Set them as object properties
Store them in arrays
Set them as variables

Question 5

Higher-order function that executes a function once for each array element

Answer 5

forEach()
var array1 = ['a', 'b', 'c'];
array1.forEach(function(element) {
  console.log(element);
});

Question 6

Higher-order function that creates a new array with the results of calling a provided function on every element in the calling array

Answer 6

map()
var array1 = [1, 4, 9, 16];
// pass a function to map
const map1 = array1.map(x => x * 2);
console.log(map1);
// expected output: Array [2, 8, 18, 32]

Question 7

Higher-order function that creates a new array with all the elements that pass the test implemented by the provided function

Answer 7

filter()
var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]

Question 8

Higher-order function that executes a provided reducer function on each element of the array resulting in a single output value

Answer 8

reduce()
const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15