Functional Programming

Question 1

Functional programming follows a few core principles:

Answer 1

Functions are independent from the state of the program or global variables. They only depend on the arguments passed into them to make a calculation

Functions try to limit any changes to the state of the program and avoid changes to the global objects holding data

Functions have minimal side effects in the program

Question 2

Pure functions mean

Answer 2

the same input always gives the same output

Question 3

Callbacks are

Answer 3

the functions that are slipped or passed into another function to decide the invocation of that function.

Question 4

First class functions are

Answer 4

Functions that can be assigned to a variable,

Passed into another function, or

Returned from another function just like any other normal value

Question 5

In JavaScript, all functions are _____ functions.

Answer 5

first class

Question 6

The functions that take a function as an argument, or return a function as a return value are called ____

Answer 6

higher order functions.

Question 7

Lambdas are

Answer 7

the functions are passed in to another function or returned from another function – those functions which gets passed in or returned

Question 8

an imperative style in programming is

Answer 8

one that gives the computer a set of statements to perform a task.

Question 9

functional programming is a form of ____

Answer 9

declarative programming. You tell the computer what you want done by calling a method or function.

Question 10

principle of functional programming is to ____

Answer 10

always declare your dependencies explicitly.

This means if a function depends on a variable or object being present, then pass that variable or object directly into the function as an argument

Question 11

map(({Title: title, imdbRating: rating}) => ({title, rating})) //does something

Answer 11

iterates over each item in an array

Returns: new array containing the results of calling the callback function on each element.

The original array doesn’t change.

Question 12

filter(obj => obj.property < value) //does

Answer 12

calls a function on each element of an array

Returns: a new array containing only the elements for which that function returns true

The original array doesn’t change.

In other words, it filters the array, based on the function passed to it.

Question 13

using concat() vs push()

Answer 13

concat doesn’t mutate the original, but push does

Question 14

sort by ascending order using arr.sort() (code)

Answer 14

function ascendingOrder(arr) {
  return arr.sort(function(a, b) {
    return a - b;
  });
}
ascendingOrder([1, 5, 2, 3, 4]);
// Returns [1, 2, 3, 4, 5]

Question 15

JavaScript’s default sorting method is by

Answer 15

string Unicode point value

Question 16

Logic of how compareFunction (callback for sort()) works

Answer 16

less than 0 for two elements a and b, then a will come before b.

greater than 0 for two elements a and b, then b will come before a.

0 for two elements a and b, then a and b will remain unchanged.

return arr.sort((a,b) => a === b ? 0: a<b></b>

Question 17

A side effect of the sort method is that it ___

Answer 17

changes the order of the elements in the original array

Question 18

One way to avoid sort() mutating the original array is to first ___

Answer 18

concatenate an empty array to the one being sorted (remember that slice and concat return a new array), then run the sort method.

Question 19

the join() method

Answer 19

join the elements of an array together to create a string. It takes an argument for the delimiter that is used to separate the array elements in the string.

Question 20

every() method

Answer 20

works with arrays to check if every element passes a particular test. It returns a Boolean value - true if all values meet the criteria, false if not.

Question 21

some() method

Answer 21

works with arrays to check if any element passes a particular test. It returns a Boolean value - true if any of the values meet the criteria, false if not.

Question 22

The arity of a function is

Answer 22

the number of arguments it requires.

Question 23

Currying a function means

Answer 23

to convert a function of N arity into N functions of arity 1.

it restructures a function so it takes one argument, then returns another function that takes the next argument, and so on

Question 24

Example code of uncurried and curried functions

Answer 24

//Un-curried function
function unCurried(x, y) {
  return x + y;
}

//Curried function
function curried(x) {
  return function(y) {
    return x + y;
  }
}
//Alternative using ES6
const curried = x => y => x + y

curried(1)(2) // Returns 3

Question 25

Currying is useful in your program if

Answer 25

you can’t supply all the arguments to a function at one time.

You can save each function call into a variable, which will hold the returned function reference that takes the next argument when it’s available. Here’s an example using the curried function in the example above:

// Call a curried function in parts:
var funcForY = curried(1);
console.log(funcForY(2)); // Prints 3

Question 26

partial application can be described as

Answer 26

applying a few arguments to a function at a time and returning another function that is applied to more arguments. Here’s an example:

//Impartial function
function impartial(x, y, z) {
  return x + y + z;
}
var partialFn = impartial.bind(this, 1, 2);
partialFn(10); // Returns 13