"title":"Introduction to the Functional Programming Challenges",
"description":[
[
"http://imgs.xkcd.com/comics/functional.png",
"XKCD web comic with one person asking why the other likes functional programming so much, and the second responding that tail recursion is its own reward.",
"Functional programming is an approach to software development based around the evaluation of functions. Like mathematics, functions in programming map input to output to produce a result. You can combine basic functions in many ways to build more and more complex programs.<br><br>Functional programming follows a few core principles:<br><br><ul><li>Functions are independent from the state of the program or global variables. They only depend on the arguments passed into them to make a calculation</li><br><li>Functions try to limit any changes to the state of the program and avoid changes to the global objects holding data</li><br><li>Functions have minimal side effects in the program</li></ul><br><br>The functional programming software development approach breaks a program into small, testable parts. This section covers basic functional programming principles in JavaScript.",
""
]],
"releasedOn":"",
"challengeSeed":[],
"tests":[],
"type":"Waypoint",
"challengeType":7,
"isRequired":false,
"titleEs":"",
"descriptionEs":[
[]
],
"titleFr":"",
"descriptionFr":[
[]
],
"titleDe":"",
"descriptionDe":[
[]
]
},
{
"id":"587d7b8d367417b2b2512b5b",
"title":"Learn About Functional Programming",
"description":[
"Functional programming is a style of programming where solutions are simple, isolated functions, without any side effects outside of the function scope.",
"<code>INPUT -> PROCESS -> OUTPUT</code>",
"Functional programming is about:",
"1) Isolated functions - there is no dependence on the state of the program, which includes global variables that are subject to change",
"2) Pure functions - the same input always gives the same output",
"3) Functions with limited side effects - any changes, or mutations, to the state of the program outside the function are carefully controlled",
"In the code editor, the <code>prepareTea</code> and <code>getTea</code> functions are already defined for you. Call the <code>getTea</code> function to get 40 cups of tea for the team, and store them in the <code>tea4TeamFCC</code> variable."
],
"challengeSeed":[
"/**",
" * A long process to prepare tea.",
" * @return {string} A cup of tea.",
" **/",
"const prepareTea = () => 'greenTea';",
"",
"/**",
" * Get given number of cups of tea.",
" * @param {number} numOfCups Number of required cups of tea.",
" * @return {Array<string>} Given amount of tea cups.",
"The FCC Team had a mood swing and now wants two types of tea: green tea and black tea. General Fact: Client mood swings are pretty common.",
"With that information, we'll need to revisit the <code>getTea</code> function from last challenge to handle various tea requests. We can modify <code>getTea</code> to accept a function as a parameter to be able to change the type of tea it prepares. This makes <code>getTea</code> more flexible, and gives the programmer more control when client requests change.",
"But first, let's cover some functional terminology:",
"<code>Callbacks</code> are the functions that are slipped or passed into another function to decide the invocation of that function. You may have seen them passed to other methods, for example in <code>filter</code>, the callback function tells JavaScript the criteria for how to filter an array.",
"Functions that can be assigned to a variable, passed into another function, or returned from another function just like any other normal value, are called <code>first class</code> functions. In JavaScript, all functions are <code>first class</code> functions.",
"The functions that take a function as an argument, or return a function as a return value are called <code>higher order</code> functions.",
"When the functions are passed in to another function or returned from another function, then those functions which gets passed in or returned can be called a <code>lambda</code>.",
"Prepare 27 cups of green tea and 13 cups of black tea and store them in <code>tea4GreenTeamFCC</code> and <code>tea4BlackTeamFCC</code> variables, respectively. Note that the <code>getTea</code> function has been modified so it now takes a function as the first argument.",
"Note: The data (the number of cups of tea) is supplied as the last argument. We'll discuss this more in later lessons."
],
"challengeSeed":[
"/**",
" * A long process to prepare green tea.",
" * @return {string} A cup of green tea.",
" **/",
"const prepareGreenTea = () => 'greenTea';",
"",
"/**",
" * A long process to prepare black tea.",
" * @return {string} A cup of black tea.",
" **/",
"const prepareBlackTea = () => 'blackTea';",
"",
"/**",
" * Get given number of cups of tea.",
" * @param {function():string} prepareTea The type of tea preparing function.",
" * @param {number} numOfCups Number of required cups of tea.",
" * @return {Array<string>} Given amount of tea cups.",
"title":"Understand the Hazards of Using Imperative Code",
"description":[
"Functional programming is a good habit. It keeps your code easy to manage, and saves you from sneaky bugs. But before we get there, let's look at an imperative approach to programming to highlight where you may have issues.",
"In English (and many other languages), the imperative tense is used to give commands. Similarly, an imperative style in programming is one that gives the computer a set of statements to perform a task.",
"Often the statements change the state of the program, like updating global variables. A classic example is writing a <code>for</code> loop that gives exact directions to iterate over the indices of an array.",
"In contrast, functional programming is a form of declarative programming. You tell the computer what you want done by calling a method or function.",
"JavaScript offers many predefined methods that handle common tasks so you don't need to write out how the computer should perform them. For example, instead of using the <code>for</code> loop mentioned above, you could call the <code>map</code> method which handles the details of iterating over an array. This helps to avoid semantic errors, like the \"Off By One Errors\" that were covered in the Debugging section.",
"Consider the scenario: you are browsing the web in your browser, and want to track the tabs you have opened. Let's try to model this using some simple object-oriented code.",
"A Window object is made up of tabs, and you usually have more than one Window open. The titles of each open site in each Window object is held in an array. After working in the browser (opening new tabs, merging windows, and closing tabs), you want to print the tabs that are still open. Closed tabs are removed from the array and new tabs (for simplicity) get added to the end of it.",
"The code editor shows an implementation of this functionality with functions for <code>tabOpen()</code>, <code>tabClose()</code>, and <code>join()</code>. The array <code>tabs</code> is part of the Window object that stores the name of the open pages.",
"Run the code in the editor. It's using a method that has side effects in the program, causing incorrect output. The final list of open tabs should be <code>['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium', 'Netflix', 'YouTube', 'Vine', 'GMail', 'Work mail', 'Docs', 'freeCodeCamp', 'new tab']</code> but the output will be slightly different.",
"title":"Avoid Mutations and Side Effects Using Functional Programming",
"description":[
"If you haven't already figured it out, the issue in the previous challenge was with the <code>splice</code> call in the <code>tabClose()</code> function. Unfortunately, <code>splice</code> changes the original array it is called on, so the second call to it used a modified array, and gave unexpected results.",
"This is a small example of a much larger pattern - you call a function on a variable, array, or an object, and the function changes the variable or something in the object.",
"One of the core principle of functional programming is to not change things. Changes lead to bugs. It's easier to prevent bugs knowing that your functions don't change anything, including the function arguments or any global variable.",
"The previous example didn't have any complicated operations but the <code>splice</code> method changed the original array, and resulted in a bug.",
"Recall that in functional programming, changing or altering things is called <code>mutation</code>, and the outcome is called a <code>side effect</code>. A function, ideally, should be a <code>pure function</code>, meaning that it does not cause any side effects.",
"Let's try to master this discipline and not alter any variable or object in our code.",
"Fill in the code for the function <code>incrementer</code> so it returns the value of the global variable <code>fixedValue</code> increased by one."
],
"challengeSeed":[
"// the global variable",
"var fixedValue = 4;",
"",
"function incrementer () {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"",
"var newValue = incrementer(); // Should equal 5",
"console.log(fixedValue); // Should print 4"
],
"tests":[
"assert(fixedValue === 4, 'message: Your function <code>incrementer</code> should not change the value of <code>fixedValue</code>.');",
"assert(newValue === 5, 'message: Your <code>incrementer</code> function should return a value that is one larger than the <code>fixedValue</code> value.');"
"title":"Pass Arguments to Avoid External Dependence in a Function",
"description":[
"The last challenge was a step closer to functional programming principles, but there is still something missing.",
"We didn't alter the global variable value, but the function <code>incrementer</code> would not work without the global variable <code>fixedValue</code> being there.",
"Another principle of functional programming is to always declare your dependencies explicitly. This means if a function depends on a variable or object being present, then pass that variable or object directly into the function as an argument.",
"There are several good consequences from this principle. The function is easier to test, you know exactly what input it takes, and it won't depend on anything else in your program.",
"This can give you more confidence when you alter, remove, or add new code. You would know what you can or cannot change and you can see where the potential traps are.",
"Finally, the function would always produce the same output for the same set of inputs, no matter what part of the code executes it.",
"Let's update the <code>incrementer</code> function to clearly declare its dependencies.",
"Write the <code>incrementer</code> function so it takes an argument, and then increases the value by one."
],
"challengeSeed":[
"// the global variable",
"var fixedValue = 4;",
"",
"// Add your code below this line",
"function incrementer () {",
" ",
" ",
" // Add your code above this line",
"}",
"",
"var newValue = incrementer(fixedValue); // Should equal 5",
"console.log(fixedValue); // Should print 4"
],
"tests":[
"assert(fixedValue === 4, 'message: Your function <code>incrementer</code> should not change the value of <code>fixedValue</code>.');",
"assert(code.match(/function\\s+?incrementer\\(.+?\\)/g), 'message: Your <code>incrementer</code> function should take a parameter.');",
"assert(newValue === 5, 'message: Your <code>incrementer</code> function should return a value that is one larger than the <code>fixedValue</code> value.');"
"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."
],
"challengeSeed":[
"// the global variable",
"var bookList = [\"The Hound of the Baskervilles\", \"On The Electrodynamics of Moving Bodies\", \"Philosophiæ Naturalis Principia Mathematica\", \"Disquisitiones Arithmeticae\"];",
"",
"/* This function should add a book to the list and return the list */",
"// New parameters should come before the bookName one",
"",
"// Add your code below this line",
"function add (bookName) {",
" ",
" return bookList.push(bookName);",
" ",
" // Add your code above this line",
"}",
"",
"/* This function should remove a book from the list and return the list */",
"// New parameters should come before the bookName one",
"",
"// Add your code below this line",
"function remove (bookName) {",
" if (bookList.indexOf(bookName) >= 0) {",
" ",
" return bookList.splice(0, 1, bookName);",
" ",
" // Add your code above this line",
" }",
"}",
"",
"var newBookList = add(bookList, 'A Brief History of Time');",
"var newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');",
"var newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');",
"",
"console.log(bookList);"
],
"tests":[
"assert(JSON.stringify(bookList) === JSON.stringify([\"The Hound of the Baskervilles\", \"On The Electrodynamics of Moving Bodies\", \"Philosophiæ Naturalis Principia Mathematica\", \"Disquisitiones Arithmeticae\"]), 'message: <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>.');",
"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']), 'message: <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>.');",
"assert(JSON.stringify(newerBookList) === JSON.stringify(['The Hound of the Baskervilles', 'Philosophiæ Naturalis Principia Mathematica', 'Disquisitiones Arithmeticae']), 'message: <code>newerBookList</code> should equal <code>[\"The Hound of the Baskervilles\", \"Philosophiæ Naturalis Principia Mathematica\", \"Disquisitiones Arithmeticae\"]</code>.');",
"assert(JSON.stringify(newestBookList) === JSON.stringify(['The Hound of the Baskervilles', 'Philosophiæ Naturalis Principia Mathematica', 'Disquisitiones Arithmeticae', 'A Brief History of Time']), 'message: <code>newestBookList</code> should equal <code>[\"The Hound of the Baskervilles\", \"Philosophiæ Naturalis Principia Mathematica\", \"Disquisitiones Arithmeticae\", \"A Brief History of Time\"]</code>.');"
],
"solutions":[],
"hints":[
"Look at how the functions are called to see the correct order of the parameters.",
"Consider using the concat method instead of push.",
"The slice method returns a new array without modifying the original."
"So far we have learned to use pure functions to avoid side effects in a program. Also, we have seen the value in having a function only depend on its input arguments.",
"This is only the beginning. As its name suggests, functional programming is centered around a theory of functions.",
"It would make sense to be able to pass them as arguments to other functions, and return a function from another function. Functions are considered <code>First Class Objects</code> in JavaScript, which means they can be used like any other object. They can be saved in variables, stored in an object, or passed as function arguments.",
"Let's start with some simple array functions, which are methods on the array object prototype. In this exercise we are looking at <code>Array.prototype.map()</code>, or more simply <code>map</code>.",
"Remember that the <code>map</code> method is a way to iterate over each item in an array. It creates a new array (without changing the original one) after applying a callback function to every element.",
"The <code>watchList</code> array holds objects with information on several movies. Use <code>map</code> to pull the title and rating from <code>watchList</code> and save the new array in the <code>rating</code> variable. The code in the editor currently uses a <code>for</code> loop to do this, replace the loop functionality with your <code>map</code> expression."
],
"challengeSeed":[
"// the global variable",
"var watchList = [",
" { ",
" \"Title\": \"Inception\",",
" \"Year\": \"2010\",",
" \"Rated\": \"PG-13\",",
" \"Released\": \"16 Jul 2010\",",
" \"Runtime\": \"148 min\",",
" \"Genre\": \"Action, Adventure, Crime\",",
" \"Director\": \"Christopher Nolan\",",
" \"Writer\": \"Christopher Nolan\",",
" \"Actors\": \"Leonardo DiCaprio, Joseph Gordon-Levitt, Ellen Page, Tom Hardy\",",
" \"Plot\": \"A thief, who steals corporate secrets through use of dream-sharing technology, is given the inverse task of planting an idea into the mind of a CEO.\",",
" \"Writer\": \"Jonathan Nolan (screenplay), Christopher Nolan (screenplay), Christopher Nolan (story), David S. Goyer (story), Bob Kane (characters)\",",
" \"Actors\": \"Christian Bale, Heath Ledger, Aaron Eckhart, Michael Caine\",",
" \"Plot\": \"When the menace known as the Joker wreaks havoc and chaos on the people of Gotham, the caped crusader must come to terms with one of the greatest psychological tests of his ability to fight injustice.\",",
" \"Writer\": \"Bob Kane (characters), David S. Goyer (story), Christopher Nolan (screenplay), David S. Goyer (screenplay)\",",
" \"Actors\": \"Christian Bale, Michael Caine, Liam Neeson, Katie Holmes\",",
" \"Plot\": \"After training with his mentor, Batman begins his fight to free crime-ridden Gotham City from the corruption that Scarecrow and the League of Shadows have cast upon it.\",",
" \"Language\": \"English, Urdu, Mandarin\",",
" \"Country\": \"USA, UK\",",
" \"Awards\": \"Nominated for 1 Oscar. Another 15 wins & 66 nominations.\",",
" \"Actors\": \"Sam Worthington, Zoe Saldana, Sigourney Weaver, Stephen Lang\",",
" \"Plot\": \"A paraplegic marine dispatched to the moon Pandora on a unique mission becomes torn between following his orders and protecting the world he feels is his home.\",",
"assert(watchList[0].Title === \"Inception\" && watchList[4].Director == \"James Cameron\", 'message: The <code>watchList</code> variable should not change.');",
"assert(!code.match(/for\\s*?\\(.+?\\)/g), 'message: Your code should not use a <code>for</code> loop.');",
"assert(code.match(/\\.map/g), 'message: Your code should use the <code>map</code> method.');",
"assert(JSON.stringify(rating) === JSON.stringify([{\"title\":\"Inception\",\"rating\":\"8.8\"},{\"title\":\"Interstellar\",\"rating\":\"8.6\"},{\"title\":\"The Dark Knight\",\"rating\":\"9.0\"},{\"title\":\"Batman Begins\",\"rating\":\"8.3\"},{\"title\":\"Avatar\",\"rating\":\"7.9\"}]), 'message: <code>rating</code> should equal <code>[{\"title\":\"Inception\",\"rating\":\"8.8\"},{\"title\":\"Interstellar\",\"rating\":\"8.6\"},{\"title\":\"The Dark Knight\",\"rating\":\"9.0\"},{\"title\":\"Batman Begins\",\"rating\":\"8.3\"},{\"title\":\"Avatar\",\"rating\":\"7.9\"}]</code>.');"
"As you have seen from applying <code>Array.prototype.map()</code>, or simply <code>map()</code> earlier, the <code>map</code> method returns an array of the same length as the one it was called on. It also doesn't alter the original array, as long as its callback function doesn't.",
"In other words, <code>map</code> is a pure function, and its output depends solely on its inputs. Plus, it takes another function as its argument.",
"It would teach us a lot about <code>map</code> to try to implement a version of it that behaves exactly like the <code>Array.prototype.map()</code> with a <code>for</code> loop or <code>Array.prototype.forEach()</code>.",
"Note: A pure function is allowed to alter local variables defined within its scope, although, it's preferable to avoid that as well.",
"Write your own <code>Array.prototype.myMap()</code>, which should behave exactly like <code>Array.prototype.map()</code>. You may use a <code>for</code> loop or the <code>forEach</code> method."
"Another useful array function is <code>Array.prototype.filter()</code>, or simply <code>filter()</code>. The <code>filter</code> method returns a new array which is at most as long as the original array, but usually has fewer items.",
"<code>Filter</code> doesn't alter the original array, just like <code>map</code>. It takes a callback function that applies the logic inside the callback on each element of the array. If an element returns true based on the criteria in the callback function, then it is included in the new array.",
"The variable <code>watchList</code> holds an array of objects with information on several movies. Use a combination of <code>filter</code> and <code>map</code> to return a new array of objects with only <code>title</code> and <code>rating</code> keys, but where <code>imdbRating</code> is greater than or equal to 8.0. Note that the rating values are saved as strings in the object and you may want to convert them into numbers to perform mathematical operations on them."
],
"challengeSeed":[
"// the global variable",
"var watchList = [",
" { ",
" \"Title\": \"Inception\",",
" \"Year\": \"2010\",",
" \"Rated\": \"PG-13\",",
" \"Released\": \"16 Jul 2010\",",
" \"Runtime\": \"148 min\",",
" \"Genre\": \"Action, Adventure, Crime\",",
" \"Director\": \"Christopher Nolan\",",
" \"Writer\": \"Christopher Nolan\",",
" \"Actors\": \"Leonardo DiCaprio, Joseph Gordon-Levitt, Ellen Page, Tom Hardy\",",
" \"Plot\": \"A thief, who steals corporate secrets through use of dream-sharing technology, is given the inverse task of planting an idea into the mind of a CEO.\",",
" \"Writer\": \"Jonathan Nolan (screenplay), Christopher Nolan (screenplay), Christopher Nolan (story), David S. Goyer (story), Bob Kane (characters)\",",
" \"Actors\": \"Christian Bale, Heath Ledger, Aaron Eckhart, Michael Caine\",",
" \"Plot\": \"When the menace known as the Joker wreaks havoc and chaos on the people of Gotham, the caped crusader must come to terms with one of the greatest psychological tests of his ability to fight injustice.\",",
" \"Writer\": \"Bob Kane (characters), David S. Goyer (story), Christopher Nolan (screenplay), David S. Goyer (screenplay)\",",
" \"Actors\": \"Christian Bale, Michael Caine, Liam Neeson, Katie Holmes\",",
" \"Plot\": \"After training with his mentor, Batman begins his fight to free crime-ridden Gotham City from the corruption that Scarecrow and the League of Shadows have cast upon it.\",",
" \"Language\": \"English, Urdu, Mandarin\",",
" \"Country\": \"USA, UK\",",
" \"Awards\": \"Nominated for 1 Oscar. Another 15 wins & 66 nominations.\",",
" \"Actors\": \"Sam Worthington, Zoe Saldana, Sigourney Weaver, Stephen Lang\",",
" \"Plot\": \"A paraplegic marine dispatched to the moon Pandora on a unique mission becomes torn between following his orders and protecting the world he feels is his home.\",",
"assert(watchList[0].Title === \"Inception\" && watchList[4].Director == \"James Cameron\", 'message: The <code>watchList</code> variable should not change.');",
"assert(code.match(/\\.filter/g), 'message: Your code should use the <code>filter</code> method.');",
"assert(!code.match(/for\\s*?\\(.+?\\)/g), 'message: Your code should not use a <code>for</code> loop.');",
"It would teach us a lot about the <code>filter</code> method if we try to implement a version of it that behaves exactly like <code>Array.prototype.filter()</code>. It can use either a <code>for</code> loop or <code>Array.prototype.forEach()</code>.",
"Note: A pure function is allowed to alter local variables defined within its scope, although, it's preferable to avoid that as well.",
"Write your own <code>Array.prototype.myFilter()</code>, which should behave exactly like <code>Array.prototype.filter()</code>. You may use a <code>for</code> loop or the <code>Array.prototype.forEach()</code> method."
"The <code>slice</code> method returns a copy of certain elements of an array. It can take two arguments, the first gives the index of where to begin the slice, the second is the index for where to end the slice (and it's non-inclusive). If the arguments are not provided, the default is to start at the beginning of the array through the end, which is an easy way to make a copy of the entire array. The <code>slice</code> method does not mutate the original array, but returns a new one.",
"Use the <code>slice</code> method in the <code>sliceArray</code> function to return part of the <code>anim</code> array given the provided <code>beginSlice</code> and <code>endSlice</code> indices. The function should return an array."
"assert(code.match(/\\.slice/g), 'message: Your code should use the <code>slice</code> method.');",
"assert(JSON.stringify(inputAnim) === JSON.stringify([\"Cat\", \"Dog\", \"Tiger\", \"Zebra\", \"Ant\"]), 'message: The <code>inputAnim</code> variable should not change.');",
"A common pattern while working with arrays is when you want to remove items and keep the rest of the array. JavaScript offers the <code>splice</code> method for this, which takes arguments for the index of where to start removing items, then the number of items to remove. If the second argument is not provided, the default is to remove items through the end. However, the <code>splice</code> method mutates the original array it is called on. Here's an example:",
"<blockquote>var cities = [\"Chicago\", \"Delhi\", \"Islamabad\", \"London\", \"Berlin\"];<br>cities.splice(3, 1); // Returns \"London\" and deletes it from the cities array<br>// cities is now [\"Chicago\", \"Delhi\", \"Islamabad\", \"Berlin\"]</blockquote>",
"As we saw in the last challenge, the <code>slice</code> method does not mutate the original array, but returns a new one which can be saved into a variable. Recall that the <code>slice</code> method takes two arguments for the indices to begin and end the slice (the end is non-inclusive), and returns those items in a new array. Using the <code>slice</code> method instead of <code>splice</code> helps to avoid any array-mutating side effects.",
"Rewrite the function <code>nonMutatingSplice</code> by using <code>slice</code> instead of <code>splice</code>. It should limit the provided <code>cities</code> array to a length of 3, and return a new array with only the first three items.",
"Do not mutate the original array provided to the function."
"assert(code.match(/\\.slice/g), 'message: Your code should use the <code>slice</code> method.');",
"assert(!code.match(/\\.splice/g), 'message: Your code should not use the <code>splice</code> method.');",
"assert(JSON.stringify(inputCities) === JSON.stringify([\"Chicago\", \"Delhi\", \"Islamabad\", \"London\", \"Berlin\"]), 'message: The <code>inputCities</code> array should not change.');",
"<code>Concatenation</code> means to join items end to end. JavaScript offers the <code>concat</code> method for both strings and arrays that work in the same way. For arrays, the method is called on one, then another array is provided as the argument to <code>concat</code>, which is added to the end of the first array. It returns a new array and does not mutate either of the original arrays. Here's an example:",
"<blockquote>[1, 2, 3].concat([4, 5, 6]);<br>// Returns a new array [1, 2, 3, 4, 5, 6]</blockquote>",
"Use the <code>concat</code> method in the <code>nonMutatingConcat</code> function to concatenate <code>attach</code> to the end of <code>original</code>. The function should return the concatenated array."
],
"challengeSeed":[
"function nonMutatingConcat(original, attach) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"var first = [1, 2, 3];",
"var second = [4, 5];",
"nonMutatingConcat(first, second);"
],
"tests":[
"assert(code.match(/\\.concat/g), 'message: Your code should use the <code>concat</code> method.');",
"assert(JSON.stringify(first) === JSON.stringify([1, 2, 3]), 'message: The <code>first</code> array should not change.');",
"assert(JSON.stringify(second) === JSON.stringify([4, 5]), 'message: The <code>second</code> array should not change.');",
"Functional programming is all about creating and using non-mutating functions.",
"The last challenge introduced the <code>concat</code> method as a way to combine arrays into a new one without mutating the original arrays. Compare <code>concat</code> to the <code>push</code> method. <code>Push</code> adds an item to the end of the same array it is called on, which mutates that array. Here's an example:",
"Change the <code>nonMutatingPush</code> function so it uses <code>concat</code> to add <code>newItem</code> to the end of <code>original</code> instead of <code>push</code>. The function should return an array."
],
"challengeSeed":[
"function nonMutatingPush(original, newItem) {",
" // Add your code below this line",
" return original.push(newItem);",
" ",
" // Add your code above this line",
"}",
"var first = [1, 2, 3];",
"var second = [4, 5];",
"nonMutatingPush(first, second);"
],
"tests":[
"assert(code.match(/\\.concat/g), 'message: Your code should use the <code>concat</code> method.');",
"assert(!code.match(/\\.push/g), 'message: Your code should not use the <code>push</code> method.');",
"assert(JSON.stringify(first) === JSON.stringify([1, 2, 3]), 'message: The <code>first</code> array should not change.');",
"assert(JSON.stringify(second) === JSON.stringify([4, 5]), 'message: The <code>second</code> array should not change.');",
"<code>Array.prototype.reduce()</code>, or simply <code>reduce()</code>, is the most general of all array operations in JavaScript. You can solve almost any array processing problem using the <code>reduce</code> method.",
"This is not the case with the <code>filter</code> and <code>map</code> methods since they do not allow interaction between two different elements of the array. For example, if you want to compare elements of the array, or add them together, <code>filter</code> or <code>map</code> could not process that.",
"The <code>reduce</code> method allows for more general forms of array processing, and it's possible to show that both <code>filter</code> and <code>map</code> can be derived as a special application of <code>reduce</code>.",
"However, before we get there, let's practice using <code>reduce</code> first.",
"The variable <code>watchList</code> holds an array of objects with information on several movies. Use <code>reduce</code> to find the average IMDB rating of the movies directed by Christopher Nolan. Recall from prior challenges how to <code>filter</code> data and <code>map</code> over it to pull what you need. You may need to create other variables, but save the final average into the variable <code>averageRating</code>. Note that the rating values are saved as strings in the object and need to be converted into numbers before they are used in any mathematical operations."
],
"challengeSeed":[
"// the global variable",
"var watchList = [",
" { ",
" \"Title\": \"Inception\",",
" \"Year\": \"2010\",",
" \"Rated\": \"PG-13\",",
" \"Released\": \"16 Jul 2010\",",
" \"Runtime\": \"148 min\",",
" \"Genre\": \"Action, Adventure, Crime\",",
" \"Director\": \"Christopher Nolan\",",
" \"Writer\": \"Christopher Nolan\",",
" \"Actors\": \"Leonardo DiCaprio, Joseph Gordon-Levitt, Ellen Page, Tom Hardy\",",
" \"Plot\": \"A thief, who steals corporate secrets through use of dream-sharing technology, is given the inverse task of planting an idea into the mind of a CEO.\",",
" \"Writer\": \"Jonathan Nolan (screenplay), Christopher Nolan (screenplay), Christopher Nolan (story), David S. Goyer (story), Bob Kane (characters)\",",
" \"Actors\": \"Christian Bale, Heath Ledger, Aaron Eckhart, Michael Caine\",",
" \"Plot\": \"When the menace known as the Joker wreaks havoc and chaos on the people of Gotham, the caped crusader must come to terms with one of the greatest psychological tests of his ability to fight injustice.\",",
" \"Writer\": \"Bob Kane (characters), David S. Goyer (story), Christopher Nolan (screenplay), David S. Goyer (screenplay)\",",
" \"Actors\": \"Christian Bale, Michael Caine, Liam Neeson, Katie Holmes\",",
" \"Plot\": \"After training with his mentor, Batman begins his fight to free crime-ridden Gotham City from the corruption that Scarecrow and the League of Shadows have cast upon it.\",",
" \"Language\": \"English, Urdu, Mandarin\",",
" \"Country\": \"USA, UK\",",
" \"Awards\": \"Nominated for 1 Oscar. Another 15 wins & 66 nominations.\",",
" \"Actors\": \"Sam Worthington, Zoe Saldana, Sigourney Weaver, Stephen Lang\",",
" \"Plot\": \"A paraplegic marine dispatched to the moon Pandora on a unique mission becomes torn between following his orders and protecting the world he feels is his home.\",",
"assert(watchList[0].Title === \"Inception\" && watchList[4].Director == \"James Cameron\", 'message: The <code>watchList</code> variable should not change.');",
"assert(code.match(/\\.reduce/g), 'message: Your code should use the <code>reduce</code> method.');",
"assert(averageRating == 8.675, 'message: The <code>averageRating</code> should equal 8.675.');",
"assert(!code.match(/for\\s*?\\(.*\\)/g), 'message: Your code should not use a <code>for</code> loop.');"
],
"solutions":[],
"hints":[
"Try using .filter() to filter the watchList by Director.",
"Try using .map() to return an array of ratings.",
"You can use Number() to convert a string into a number."
"The <code>sort</code> method sorts the elements of an array according to the callback function.",
"For example:",
"<blockquote>function ascendingOrder(arr) {<br> return arr.sort(function(a, b) {<br> return a - b;<br> });<br>}<br>ascendingOrder([1, 5, 2, 3, 4]);<br>// Returns [1, 2, 3, 4, 5]<br><br>function reverseAlpha(arr) {<br> return arr.sort(function(a, b) {<br> return a < b;<br> });<br>}<br>reverseAlpha(['l', 'h', 'z', 'b', 's']);<br>// Returns ['z', 's', 'l', 'h', 'b']</blockquote>",
"Note: It's encouraged to provide a callback function to specify how to sort the array items. JavaScript's default sorting method is by string Unicode point value, which may return unexpected results.",
"title":"Return a Sorted Array Without Changing the Original Array",
"description":[
"A side effect of the <code>sort</code> method is that it changes the order of the elements in the original array. In other words, it mutates the array in place. One way to avoid this is to first concatenate an empty array to the one being sorted (remember that <code>concat</code> returns a new array), then run the <code>sort</code> method.",
"Use the <code>sort</code> method in the <code>nonMutatingSort</code> function to sort the elements of an array in ascending order. The function should return a new array, and not mutate the <code>globalArray</code> variable."
],
"challengeSeed":[
"var globalArray = [5, 6, 3, 2, 9];",
"function nonMutatingSort(arr) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"nonMutatingSort(globalArray);"
],
"tests":[
"assert(code.match(/\\.sort/g), 'message: Your code should use the <code>sort</code> method.');",
"assert(code.match(/\\.concat/g), 'message: Your code should use the <code>concat</code> method.');",
"assert(JSON.stringify(globalArray) === JSON.stringify([5, 6, 3, 2, 9]), 'message: The <code>globalArray</code> variable should not change.');",
"The <code>split</code> method splits a string into an array of strings. It takes an argument for the delimiter, which can be a character to use to break up the string or a regular expression. For example, if the delimiter is a space, you get an array of words, and if the delimiter is an empty string, you get an array of each character in the string.",
"Here are two examples that split one string by spaces, then another by digits using a regular expression:",
"Use the <code>split</code> method inside the <code>splitify</code> function to split <code>str</code> into an array of words. The function should return the array. Note that the words are not always separated by spaces, and the array should not contain punctuation."
],
"challengeSeed":[
"function splitify(str) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"splitify(\"Hello World,I-am code\");"
],
"tests":[
"assert(code.match(/\\.split/g), 'message: Your code should use the <code>split</code> method.');",
"The <code>join</code> method is used to join the elements of an array together to create a string. It takes an argument for the delimiter that is used to separate the array elements in the string.",
"Use the <code>join</code> method (among others) inside the <code>sentensify</code> function to make a sentence from the words in the string <code>str</code>. The function should return a string. For example, \"I-like-Star-Wars\" would be converted to \"I like Star Wars\". For this challenge, do not use the <code>replace</code> method."
],
"challengeSeed":[
"function sentensify(str) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"sentensify(\"May-the-force-be-with-you\");"
],
"tests":[
"assert(code.match(/\\.join/g), 'message: Your code should use the <code>join</code> method.');",
"assert(!code.match(/\\.replace/g), 'message: Your code should not use the <code>replace</code> method.');",
"assert(typeof sentensify(\"May-the-force-be-with-you\") === \"string\", 'message: <code>sentensify(\"May-the-force-be-with-you\")</code> should return a string.');",
"assert(sentensify(\"May-the-force-be-with-you\") === \"May the force be with you\", 'message: <code>sentensify(\"May-the-force-be-with-you\")</code> should return <code>\"May the force be with you\"</code>.');",
"assert(sentensify(\"The.force.is.strong.with.this.one\") === \"The force is strong with this one\", 'message: <code>sentensify(\"The.force.is.strong.with.this.one\")</code> should return <code>\"The force is strong with this one\"</code>.');",
"assert(sentensify(\"There,has,been,an,awakening\") === \"There has been an awakening\", 'message: <code>sentensify(\"There,has,been,an,awakening\")</code> should return <code>\"There has been an awakening\"</code>.');"
],
"solutions":[],
"hints":[
"First try to split the given string before applying the join method."
"title":"Apply Functional Programming to Convert Strings to URL Slugs",
"description":[
"The last several challenges covered a number of useful array and string methods that follow functional programming principles. We've also learned about <code>reduce</code>, which is a powerful method used to reduce problems to simpler forms. From computing averages to sorting, any array operation can be achieved by applying it. Recall that <code>map</code> and <code>filter</code> are special cases of <code>reduce</code>.",
"Let's combine what we've learned to solve a practical problem.",
"Many content management sites (CMS) have the titles of a post added to part of the URL for simple bookmarking purposes. For example, if you write a Medium post titled \"Stop Using Reduce\", it's likely the URL would have some form of the title string in it (\".../stop-using-reduce\"). You may have already noticed this on the freeCodeCamp site.",
"Fill in the <code>urlSlug</code> function so it converts a string <code>title</code> and returns the hyphenated version for the URL. You can use any of the methods covered in this section, and don't use <code>replace</code>. Here are the requirements:",
"The input is a string with spaces and title-cased words",
"The output is a string with the spaces between words replaced by a hyphen (<code>-</code>)",
"var winterComing = urlSlug(globalTitle); // Should be \"winter-is-coming\""
],
"tests":[
"assert(globalTitle === \"Winter Is Coming\", 'message: The <code>globalTitle</code> variable should not change.');",
"assert(!code.match(/\\.replace/g), 'message: Your code should not use the <code>replace</code> method for this challenge.');",
"assert(urlSlug(\"Winter Is Coming\") === \"winter-is-coming\", 'message: <code>urlSlug(\"Winter Is Coming\")</code> should return <code>\"winter-is-coming\"</code>.');",
"assert(urlSlug(\" Winter Is Coming\") === \"winter-is-coming\", 'message: <code>urlSlug(\" Winter Is Coming\")</code> should return <code>\"winter-is-coming\"</code>.');",
"assert(urlSlug(\"A Mind Needs Books Like A Sword Needs A Whetstone\") === \"a-mind-needs-books-like-a-sword-needs-a-whetstone\", 'message: <code>urlSlug(\"A Mind Needs Books Like A Sword Needs A Whetstone\")</code> should return <code>\"a-mind-needs-books-like-a-sword-needs-a-whetstone\"</code>.');",
"assert(urlSlug(\"Hold The Door\") === \"hold-the-door\", 'message: <code>urlSlug(\"Hold The Door\")</code> should return <code>\"hold-the-door\"</code>.');"
],
"solutions":[],
"hints":[
"When several spaces in a row are split by space, it puts an empty string in the array.",
"You can use the .toLowerCase() method to make the title all lower case."
"The <code>every</code> method works with arrays to check if <em>every</em> element passes a particular test. It returns a Boolean value - <code>true</code> if all values meet the criteria, <code>false</code> if not.",
"For example, the following code would check if every element in the <code>numbers</code> array is less than 10:",
"Use the <code>every</code> method inside the <code>checkPositive</code> function to check if every element in <code>arr</code> is positive. The function should return a Boolean value."
],
"challengeSeed":[
"function checkPositive(arr) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"checkPositive([1, 2, 3, -4, 5]);"
],
"tests":[
"assert(code.match(/\\.every/g), 'message: Your code should use the <code>every</code> method.');",
"The <code>some</code> method works with arrays to check if <em>any</em> element passes a particular test. It returns a Boolean value - <code>true</code> if any of the values meet the criteria, <code>false</code> if not.",
"For example, the following code would check if any element in the <code>numbers</code> array is less than 10:",
"Use the <code>some</code> method inside the <code>checkPositive</code> function to check if any element in <code>arr</code> is positive. The function should return a Boolean value."
],
"challengeSeed":[
"function checkPositive(arr) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"checkPositive([1, 2, 3, -4, 5]);"
],
"tests":[
"assert(code.match(/\\.some/g), 'message: Your code should use the <code>some</code> method.');",
"title":"Introduction to Currying and Partial Application",
"description":[
"The <code>arity</code> of a function is the number of arguments it requires. <code>Currying</code> a function means to convert a function of N <code>arity</code> into N functions of <code>arity</code> 1.",
"In other words, it restructures a function so it takes one argument, then returns another function that takes the next argument, and so on.",
"Here's an example:",
"<blockquote>//Un-curried function<br>function unCurried(x, y, z) {<br> return x + y + z;<br>}<br><br>//Curried function<br>function curried(x) {<br> return function(y) {<br> return x + y;<br> }<br>}<br>curried(1)(2) // Returns 3</blockquote>",
"This is useful in your program if you can't supply all the arguments to a function at one time. You can save each function call into a variable, which will hold the returned function reference that takes the next argument when it's available. Here's an example using the <code>curried</code> function in the example above:",
"<blockquote>// Call a curried function in parts:<br>var funcForY = curried(1);<br>var funcForZ = funcForY(2);<br>console.log(funcForZ(3)); // Prints 6</blockquote>",
"Similarly, <code>partial application</code> can be described as applying a few arguments to a function at a time and returning another function that is applied to more arguments.",
"Here's an example:",
"<blockquote>//Impartial function<br>function impartial(x, y, z) {<br> return x + y + z;<br>}<br>var partialFn = impartial.bind(this, 1, 2);<br>partialFn(10); // Returns 13</blockquote>",
"Fill in the body of the <code>add</code> function so it uses currying to add parameters <code>x</code>, <code>y</code>, and <code>z</code>."
],
"challengeSeed":[
"function add(x) {",
" // Add your code below this line",
" ",
" ",
" // Add your code above this line",
"}",
"add(10)(20)(30);"
],
"tests":[
"assert(add(10)(20)(30) === 60, 'message: <code>add(10)(20)(30)</code> should return <code>60</code>.');",
"assert(add(1)(2)(3) === 6, 'message: <code>add(1)(2)(3)</code> should return <code>6</code>.');",
"assert(add(11)(22)(33) === 66, 'message: <code>add(11)(22)(33)</code> should return <code>66</code>.');",
"assert(code.match(/[xyz]\\s*?\\+\\s*?[xyz]\\s*?\\+\\s*?[xyz]/g), 'message: Your code should include a final statement that returns <code>x + y + z</code>.');"
