142 lines
4.7 KiB
Markdown
142 lines
4.7 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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forumTopicId: 301235
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dashedName: refactor-global-variables-out-of-functions
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---
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# --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. Hint: using something like `var newArr = arrVar`, where `arrVar` is an array will simply create a reference to the existing variable and not a copy. So changing a value in `newArr` would change the value in `arrVar`.
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2) Declare function parameters - any computation inside a function depends only on the arguments passed to the function, 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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# --instructions--
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Rewrite the code so the global array `bookList` is not changed inside either function. The `add` function should add the given `bookName` to the end of the array passed to it and return a new array (list). The `remove` function should remove the given `bookName` from the array passed to it.
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**Note:** Both functions should return an array, and any new parameters should be added before the `bookName` parameter.
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# --hints--
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`bookList` should not change and still equal `["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]`.
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```js
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assert(
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JSON.stringify(bookList) ===
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JSON.stringify([
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'The Hound of the Baskervilles',
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'On The Electrodynamics of Moving Bodies',
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'Philosophiæ Naturalis Principia Mathematica',
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'Disquisitiones Arithmeticae'
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])
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);
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```
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`newBookList` should equal `["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]`.
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```js
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assert(
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JSON.stringify(newBookList) ===
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JSON.stringify([
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'The Hound of the Baskervilles',
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'On The Electrodynamics of Moving Bodies',
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'Philosophiæ Naturalis Principia Mathematica',
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'Disquisitiones Arithmeticae',
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'A Brief History of Time'
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])
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);
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```
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`newerBookList` should equal `["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"]`.
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```js
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assert(
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JSON.stringify(newerBookList) ===
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JSON.stringify([
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'The Hound of the Baskervilles',
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'Philosophiæ Naturalis Principia Mathematica',
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'Disquisitiones Arithmeticae'
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])
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);
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```
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`newestBookList` should equal `["The Hound of the Baskervilles", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae", "A Brief History of Time"]`.
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```js
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assert(
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JSON.stringify(newestBookList) ===
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JSON.stringify([
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'The Hound of the Baskervilles',
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'Philosophiæ Naturalis Principia Mathematica',
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'Disquisitiones Arithmeticae',
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'A Brief History of Time'
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])
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);
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```
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# --seed--
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## --seed-contents--
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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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// Change code below this line
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function add (bookName) {
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bookList.push(bookName);
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return bookList;
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// Change code above this line
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}
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// Change code below this line
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function remove (bookName) {
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var book_index = bookList.indexOf(bookName);
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if (book_index >= 0) {
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bookList.splice(book_index, 1);
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return bookList;
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// Change 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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# --solutions--
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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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function add (bookList, bookName) {
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return [...bookList, bookName];
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}
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function remove (bookList, bookName) {
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const bookListCopy = [...bookList];
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const bookNameIndex = bookList.indexOf(bookName);
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if (bookNameIndex >= 0) {
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bookListCopy.splice(bookNameIndex, 1);
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}
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return bookListCopy;
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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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```
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