JavaScript Advanced Functions: First-Class Functions Lab

Learning Goals

• Assign functions to a variable.
• Store functions in a data structure.
• Write functions that return other functions.
• Pass a function to another function.
• Call a function returned by another function.

Introduction

Functions are a very important part of JavaScript, and you will use them all the time. Without functions, we wouldn't get anything done! In this lab, we'll take a look at how we can use functions as first-class objects to pass them around, store them in variables and data structures, and return them from other functions.

For this lab, you will continue working on functions for our scooter-taxi client, Scuber.

Instructions

Using the tests to guide you, create the following deliverables:

• returnFirstTwoDrivers() — Declare the variable returnFirstTwoDrivers with const and assign an anonymous function to it. The assigned function should take one argument, an array containing the names of Scuber's drivers, and return a new array containing the first two drivers in the array:

returnFirstTwoDrivers(['Antonia', 'Nuru', 'Amari', 'Mo'])
// => ['Antonia', 'Nuru']

• returnLastTwoDrivers() — Declare a variable with const that is assigned an anonymous function. The assigned function should take one argument, an array containing the names of Scuber's drivers, and return a new array containing the last two drivers in the array:

returnLastTwoDrivers(['Antonia', 'Nuru', 'Amari', 'Mo'])
// => ['Amari', 'Mo']

• selectingDrivers — This is an array containing two elements: the two functions that we previously defined (returnFirstTwoDrivers() and returnLastTwoDrivers()).
• createFareMultiplier() — This is a higher-order function that takes in one argument, an integer, and returns a function that will multiply a fare for a ride accordingly. For example, if createFareMultiplier() receives an argument of 4, it will return a function that takes in a fare as an argument and quadruples the fare.
• fareDoubler() — Declare a variable with const and assign a function returned by createFareMultiplier() to it. Invoke createFareMultiplier() in such a way that the new fareDoubler() function accepts a fare as its lone argument and doubles it.
• fareTripler() — Declare a variable with const and assign a function returned by createFareMultiplier() to it. Invoke createFareMultiplier() in such a way that the new fareTripler() function accepts a fare as its lone argument and triples it.
• selectDifferentDrivers() — This function takes two arguments, an array of the names of Scuber's drivers and either the returnFirstTwoDrivers() or returnLastTwoDrivers() function. Based on these two arguments, selectDifferentDrivers() will return either the first two drivers or the last two drivers.

Resources

• Wikipedia: First-class function
• MDN: Functions
• TypeOfNaN: What is a Higher-Order Function?