JS-Exercise-Closures-Callbacks-ArrayMethods

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JS-Exercise-Closures-Callbacks-ArrayMethods

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An exercise on Closures, Callbacks and Array Methods.

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# 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](https://www.rulesofsport.com/sports/baseball.html).

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

![Fenway Scoreboard](https://storage.googleapis.com/afs-prod/media/media:e959506330fd4e5890023c93cfbaac55/800.jpeg)

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 repo and add TL as collaborator on Github
2. Clone _your_ fork (not Lambda's repo by mistake!)
3. `cd` into your newly cloned repository
4. Create a new branch by typing `git checkout -b <firstName-lastName>`
5. Work on your branch, push commits and create PR as usual

### Task 2a - MVP code

Find the file `index.js` and complete the tasks until your tests are passing.

### 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.

```js
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. Predict the output of the code below and explain why this is the output using what you learned today. When you're ready for answers, view an explanation [here](https://www.coderbyte.com/algorithm/3-common-javascript-closure-questions

```js
(function(){
  var a = b = 3;
})();
console.log("a defined? " + (typeof a !== 'undefined'));
console.log("b defined? " + (typeof b !== 'undefined'));
```

2. 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](https://www.coderbyte.com/algorithm/3-common-javascript-closure-questions)).

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

3. 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](https://css-tricks.com/javascript-scope-closures/)

🧠 ["I never Understood Closures" Blog](https://medium.com/dailyjs/i-never-understood-javascript-closures-9663703368e8)

## Submission Format

Follow these steps for completing your project.

- [ ] Submit a pull request to merge <firstName-lastName> Branch into master (student's  Repo). **Please don't merge your own pull request**
- [ ] Add your Team Lead as a reviewer on the pull request
- [ ] Your Team Lead will count the project as complete by merging the branch back into master

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