Scope and Closure Challenge

The module challenge is the afternoon project or assignment that students work through independently. This expands on the guided project completed earlier with the instructor.

JavaScript Foundations

Scope and Closures

Objectives

• Explain function scope
• Describe what closure is, how closure is created in a program and why it is important to understand closures in JavaScript

Introduction

This challenge focuses on both scope and closures.

In this challenge you will be working to build a scoreboard (in the console) that takes randomly generated data and keeps track of a game's progress. If you're not familiar with the rules of baseball what you need to know is this: there are 9 innings and teams take turns "at-bat." Teams can only score while they are at bat. A team stops being at bat once they have gotten 3 outs by either striking out or through game play. You can read more about baseball rules here.

A scoreboard in a major league stadium looks something like this. In fact, the scoreboard at Fenway Park in Boston is actually quite famous.

There are layers upon layers of nested functions within the game of baseball. Your challenge today will be to work through tasks associated with these layers, and ultimately to produce a scoreboard that logs in the console.

Instructions

Task 1 - Set Up Project and Tests

1. Fork the repo
2. Clone your forked version of the repo
3. cd into your repo and create a branch with your first and last name
4. open the terminal in your vs code and type npm install
5. next type npm run test:watch in your terminal
6. Complete your work making regular commits, once you have all your tests passing and you are ready to submit your work please see canvas for instructions on how to submit

Task 2a - MVP code

Find the file index.js and complete the tasks.

Task 2b - Written questions

Edit the ReadMe file with your answers.

1. In your own words, define closure (1-2 sentences).
2. Study the following code, then answer the questions below.

function personalDice(name){
  return function(){
      // generate random number between 1 and 6
    const newRoll = Math.floor(Math.random() * 6);
    console.log(`${name} rolled a ${newRoll}`)
  }
}

const dansRoll = personalDice("Dan");

const zoesRoll = personalDice("Zoe");


dansRoll();
dansRoll();

a. Where is closure used in this code? How can you tell? b. Compare and contrast calling dansRoll the first and second time. What is always the same? What could change? c. What is the lexical scope of newRoll?

Task 3 - Stretch Goals

After you have completed the requirements, create a new file called stretch.js and practice more with closures. There are no tests for these problems.

See if you can complete one or more of the following challenges:

1. Write a function that would allow you to do this using a closure. (This is another interview question we've seen before - when you're ready for answers, view an explanation here).

var addSix = createBase(6);
addSix(10); // returns 16
addSix(21); // returns 27

2. Research the differences between functional programming and object oriented programming. Then, describe the pros and cons of functional programming vs object-oriented programming. This is a common interview question and great practice!

Resources

📚 Scope and Closures Guide

🧠 "I never Understood Closures" Blog

Submission Format

Please see Canvas for cohort specific submission instructions