91 lines
4.9 KiB
Markdown
91 lines
4.9 KiB
Markdown
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---
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id: 587d7b8f367417b2b2512b60
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title: Refactor Global Variables Out of Functions
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challengeType: 1
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---
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## Description
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<section id='description'>
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So far, we have seen two distinct principles for functional programming:
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1) Don't alter a variable or object - create new variables and objects and return them if need be from a function.
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2) Declare function arguments - any computation inside a function depends only on the arguments, and not on any global object or variable.
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Adding one to a number is not very exciting, but we can apply these principles when working with arrays or more complex objects.
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</section>
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## Instructions
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<section id='instructions'>
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Refactor (rewrite) the code so the global array <code>bookList</code> is not changed inside either function. The <code>add</code> function should add the given <code>bookName</code> to the end of an array. The <code>remove</code> function should remove the given <code>bookName</code> from an array. Both functions should return an array, and any new parameters should be added before the <code>bookName</code> one.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: '<code>bookList</code> should not change and still equal <code>["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]</code>.'
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testString: 'assert(JSON.stringify(bookList) === JSON.stringify(["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]), ''<code>bookList</code> should not change and still equal <code>["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]</code>.'');'
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- text: '<code>newBookList</code> should equal <code>["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]</code>.'
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testString: 'assert(JSON.stringify(newBookList) === JSON.stringify([''The Hound of the Baskervilles'', ''On The Electrodynamics of Moving Bodies'', ''Philosophiæ Naturalis Principia Mathematica'', ''Disquisitiones Arithmeticae'', ''A Brief History of Time'']), ''<code>newBookList</code> should equal <code>["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]</code>.'');'
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- text: '<code>newerBookList</code> should equal <code>["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]</code>.'
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testString: 'assert(JSON.stringify(newerBookList) === JSON.stringify([''The Hound of the Baskervilles'', ''Philosophiæ Naturalis Principia Mathematica'', ''Disquisitiones Arithmeticae'']), ''<code>newerBookList</code> should equal <code>["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]</code>.'');'
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- text: '<code>newestBookList</code> should equal <code>["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]</code>.'
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testString: 'assert(JSON.stringify(newestBookList) === JSON.stringify([''The Hound of the Baskervilles'', ''Philosophiæ Naturalis Principia Mathematica'', ''Disquisitiones Arithmeticae'', ''A Brief History of Time'']), ''<code>newestBookList</code> should equal <code>["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]</code>.'');'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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// the global variable
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var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];
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/* This function should add a book to the list and return the list */
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// New parameters should come before the bookName one
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// Add your code below this line
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function add (bookName) {
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return bookList.push(bookName);
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// Add your code above this line
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}
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/* This function should remove a book from the list and return the list */
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// New parameters should come before the bookName one
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// Add your code below this line
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function remove (bookName) {
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if (bookList.indexOf(bookName) >= 0) {
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return bookList.splice(0, 1, bookName);
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// Add your code above this line
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}
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}
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var newBookList = add(bookList, 'A Brief History of Time');
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var newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
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var newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');
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console.log(bookList);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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