Version: 2020fa

Assignment 3

For this assignment, we will be taking a nice break from Express and Firebase to learn about some cool JavaScript fundamentals!

ALL questions in this assignment MUST be done using .map, .filter, or .reduce. We will give you no credit for an approach that is not functional.

ALL functions must also be defined using arrow functions:

(params) => {
// function body

You must write your functions from the starter code. You are not allowed to change the function signature.

Question 1#

Write a function, myMean, that takes in an array of numbers and returns the mean.

Starter code:

export const myMean = (array: number[]): number => {
/* TODO: add your code */

Question 2#

Write a function, getPrimes, that takes in an array of numbers and returns a new array containing only the elements that are primes. Reminder: prime numbers are natural numbers larger than 1 that can only be divisible by itself and 1. Don't worry about efficiency! It's ok to brute force this :)

Example: getPrimes([1, 5, 16, 3]) should return [5, 3].

Starter code:

export const getPrimes = (array: number[]): number[] => {
/* TODO: add your code */

Question 3#

Write a function, partition, that takes in an array of numbers and a function belongToGroup1, and returns an object of two arrays group1 and group2.

If belongToGroup1 returns true, then the element should go into group1. If belongToGroup1 returns false, then the element should go into group2.


partition([1, 2, 3, 4, 5, 6], (n) => n % 3 === 0); // { group1: [3, 6], group2: [1, 2, 4, 5] }
partition([1, 2, 3, 4, 5, 6], (n) => n % 2 === 0); // { group1: [2, 4, 6], group2: [1, 3, 5] }

Starter code:

export const partition = (
array: number[],
belongToGroup1: (element: number) => boolean
): { group1: number[]; group2: number[] } => {
/* TODO: add your code */

Question 4#

Write a function, makeSentences, that takes in an array of objects in the format {name: string, age: number, breed: string} and maps it to an array of sentences in the format "name is age years old, and is a breed."

Please use object destructuring to get object fields.


A "prototype" is an instance of an object in JavaScript/TypeScript. In documentation, methods are often denoted like: Type.prototype.method()

Remember, anything in JavaScript/TypeScript can be an object!

So, we can do: 5.toExponential(10) or let x = 5; x.toExponential()

Your goal is to display "5 years" for the value 5.6

Take a look at this documentation and choose an appropriate method to use!


const doggos = [
{ name: 'Sparky', age: 3.3, breed: 'Pomeranian Husky' },
{ name: 'Oreo', age: 5.4, breed: 'Dalmatian' },
{ name: 'Stella', age: 4.3, breed: 'Alaskan Klee Kai' },

should output

'Sparky is 3 years old and is a Pomeranian Husky',
'Oreo is 5 years old and is a Dalmatian',
'Stella is 4 years old and is a Alaskan Klee Kai',

Starter code:

// TODO: You should replace this any with an accurate object type in your submission!
type Doggo = any;
export const makeSentences = (array: Doggo[]): string[] => {
/* TODO: add your code */

Optional Challenge: In English, "a" becomes "an" before vowels. Create a function such that makeCorrectSentences(doggos) correctly handles this case.


Please submit to CMS your index.ts file containing your implementations of each of the functions described above.