feat(curriculum): introduce let and const earlier (#43133)

* fix: move "Explore Differences Between..." to basic JS, update seed and tests

* fix: resequence "Declare String Variables"

* fix: move "Declare a Read-Only Variable..." to basic JS, update seed and tests

* fix: revert changes to non-English "Explore Differences Between..." test text

* fix: revert test strings, solutions, and seeds for non-English challenges

* fix: update "Declare String Variables" description

* fix: sync quotation marks in description and seed

* fix: modify note in "Declare a Read-Only..." challenge

* fix: update operator and compound assignment challenges

* fix: update string challenges

* fix: update array and array method challenges

* fix: update function and scope challenges, resequence slightly

* fix: "Word Blanks" solution

* fix: add spacing to seed

* fix: concatenating += challenge spacing

* fix: appending variables to strings spacing

* fix: find the length of a string spacing

* fix: removed instances of removedFromMyArray = 0

* fix: switch challenges

* fix: function argument and param spacing

* fix: update counting cards, object challenges, and record collection

* fix: finish rest of Basic JS section

* fix: introducing else statements solution

* fix: update spacing and wording

* fix: update wording for const challenge

* fix: update functional programming challenges

* fix: intermediate algorithms and cert challenges

* fix: revert some spacing and remove comments for fp challenge solutions

* feat: add notes with links to moved let and const challenges in first two es6 challenges

* fix: update es6 intro text

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/concatenating-strings-with-the-plus-equals-operator.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/finding-a-remainder-in-javascript.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/global-scope-and-functions.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/iterate-through-an-array-with-a-for-loop.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/iterate-through-an-array-with-a-for-loop.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/implement-map-on-a-prototype.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* Update curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/declare-a-read-only-variable-with-the-const-keyword.md

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

* fix: concatenating strings with plus operator seed

* fix: add comments back to Declare a Read-Only Variable... seed

* feat: add es6 to basic javascript redirect tests for let and const challenges

* fix: revert "Concatenating Strings with Plus Operator" seed

* fix: move test file to cypress/integration/learn/redirects, separate redirect tests

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/add-elements-to-the-end-of-an-array-using-concat-instead-of-push.md

@@ -13,7 +13,7 @@ Functional programming is all about creating and using non-mutating functions.
 The last challenge introduced the `concat` method as a way to combine arrays into a new one without mutating the original arrays. Compare `concat` to the `push` method. `push` adds an item to the end of the same array it is called on, which mutates that array. Here's an example:
 
 ```js
-var arr = [1, 2, 3];
+const arr = [1, 2, 3];
 arr.push([4, 5, 6]);
 ```
 
@@ -71,8 +71,9 @@ function nonMutatingPush(original, newItem) {
 
   // Only change code above this line
 }
-var first = [1, 2, 3];
-var second = [4, 5];
+
+const first = [1, 2, 3];
+const second = [4, 5];
 nonMutatingPush(first, second);
 ```
 
@@ -82,7 +83,6 @@ nonMutatingPush(first, second);
 function nonMutatingPush(original, newItem) {
   return original.concat(newItem);
 }
-var first = [1, 2, 3];
-var second = [4, 5];
-nonMutatingPush(first, second);
+const first = [1, 2, 3];
+const second = [4, 5];
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/apply-functional-programming-to-convert-strings-to-url-slugs.md

@@ -77,7 +77,6 @@ function urlSlug(title) {
 # --solutions--
 
 ```js
-// Only change code below this line
 function urlSlug(title) {
   return title.trim().split(/\s+/).join("-").toLowerCase();
 }

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/avoid-mutations-and-side-effects-using-functional-programming.md

@@ -57,9 +57,9 @@ Your `incrementer` function should return a value based on the global `fixedValu
 
 ```js
 // The global variable
-var fixedValue = 4;
+let fixedValue = 4;
 
-function incrementer () {
+function incrementer() {
   // Only change code below this line
 
 
@@ -70,7 +70,7 @@ function incrementer () {
 # --solutions--
 
 ```js
-var fixedValue = 4
+let fixedValue = 4
 
 function incrementer() {
   return fixedValue + 1

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/combine-an-array-into-a-string-using-the-join-method.md

@@ -13,8 +13,8 @@ The `join` method is used to join the elements of an array together to create a
 Here's an example:
 
 ```js
-var arr = ["Hello", "World"];
-var str = arr.join(" ");
+const arr = ["Hello", "World"];
+const str = arr.join(" ");
 ```
 
 `str` would have a value of the string `Hello World`.
@@ -76,6 +76,7 @@ function sentensify(str) {
 
   // Only change code above this line
 }
+
 sentensify("May-the-force-be-with-you");
 ```
 
@@ -83,8 +84,6 @@ sentensify("May-the-force-be-with-you");
 
 ```js
 function sentensify(str) {
-  // Only change code below this line
   return str.split(/\W/).join(' ');
-  // Only change code above this line
 }
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/combine-two-arrays-using-the-concat-method.md

@@ -60,8 +60,9 @@ function nonMutatingConcat(original, attach) {
 
   // Only change code above this line
 }
-var first = [1, 2, 3];
-var second = [4, 5];
+
+const first = [1, 2, 3];
+const second = [4, 5];
 nonMutatingConcat(first, second);
 ```
 
@@ -69,11 +70,8 @@ nonMutatingConcat(first, second);
 
 ```js
 function nonMutatingConcat(original, attach) {
-  // Only change code below this line
   return original.concat(attach);
-  // Only change code above this line
 }
-var first = [1, 2, 3];
-var second = [4, 5];
-nonMutatingConcat(first, second);
+const first = [1, 2, 3];
+const second = [4, 5];
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/implement-map-on-a-prototype.md

@@ -38,17 +38,17 @@ assert(!code.match(/\.?[\s\S]*?map/g));
 
 ```js
 // The global variable
-var s = [23, 65, 98, 5];
+const s = [23, 65, 98, 5];
 
 Array.prototype.myMap = function(callback) {
-  var newArray = [];
+  const newArray = [];
   // Only change code below this line
 
   // Only change code above this line
   return newArray;
 };
 
-var new_s = s.myMap(function(item) {
+const new_s = s.myMap(function(item) {
   return item * 2;
 });
 ```
@@ -56,20 +56,17 @@ var new_s = s.myMap(function(item) {
 # --solutions--
 
 ```js
-// the global Array
-var s = [23, 65, 98, 5];
+const s = [23, 65, 98, 5];
 
 Array.prototype.myMap = function(callback) {
-  var newArray = [];
-  // Only change code below this line
-  for (var elem of this) {
+  const newArray = [];
+  for (const elem of this) {
     newArray.push(callback(elem));
   }
-  // Only change code above this line
   return newArray;
 };
 
-var new_s = s.myMap(function(item) {
+const new_s = s.myMap(function(item) {
   return item * 2;
 });
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/implement-the-filter-method-on-a-prototype.md

@@ -34,16 +34,16 @@ assert(!code.match(/\.?[\s\S]*?filter/g));
 
 ```js
 // The global variable
-var s = [23, 65, 98, 5];
+const s = [23, 65, 98, 5];
 
 Array.prototype.myFilter = function(callback) {
   // Only change code below this line
-  var newArray = [];
+  const newArray = [];
   // Only change code above this line
   return newArray;
 };
 
-var new_s = s.myFilter(function(item) {
+const new_s = s.myFilter(function(item) {
   return item % 2 === 1;
 });
 ```
@@ -51,20 +51,17 @@ var new_s = s.myFilter(function(item) {
 # --solutions--
 
 ```js
-// the global Array
-var s = [23, 65, 98, 5];
+const s = [23, 65, 98, 5];
 
 Array.prototype.myFilter = function(callback) {
-  var newArray = [];
-  // Only change code below this line
+  const newArray = [];
   for (let i = 0; i < this.length; i++) {
     if (callback(this[i])) newArray.push(this[i]);
   }
-  // Only change code above this line
   return newArray;
 };
 
-var new_s = s.myFilter(function(item) {
+const new_s = s.myFilter(function(item) {
   return item % 2 === 1;
 });
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/introduction-to-currying-and-partial-application.md

@@ -35,7 +35,7 @@ curried(1)(2)
 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 curried function in the example above:
 
 ```js
-var funcForY = curried(1);
+const funcForY = curried(1);
 console.log(funcForY(2)); // 3
 ```
 
@@ -45,7 +45,8 @@ Similarly, <dfn>partial application</dfn> can be described as applying a few arg
 function impartial(x, y, z) {
   return x + y + z;
 }
-var partialFn = impartial.bind(this, 1, 2);
+
+const partialFn = impartial.bind(this, 1, 2);
 partialFn(10); // 13
 ```
 
@@ -90,6 +91,7 @@ function add(x) {
 
   // Only change code above this line
 }
+
 add(10)(20)(30);
 ```
 

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/pass-arguments-to-avoid-external-dependence-in-a-function.md

@@ -53,10 +53,10 @@ assert(__newValue === 5);
 
 ```js
 // The global variable
-var fixedValue = 4;
+let fixedValue = 4;
 
 // Only change code below this line
-function incrementer () {
+function incrementer() {
 
 
   // Only change code above this line
@@ -66,15 +66,9 @@ function incrementer () {
 # --solutions--
 
 ```js
-// The global variable
-var fixedValue = 4;
+let fixedValue = 4;
 
-// Only change code below this line
-function incrementer (fixedValue) {
+function incrementer(fixedValue) {
   return fixedValue + 1;
-
-  // Only change code above this line
 }
-
-  
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/refactor-global-variables-out-of-functions.md

@@ -10,7 +10,7 @@ dashedName: refactor-global-variables-out-of-functions
 
 So far, we have seen two distinct principles for functional programming:
 
-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`.
+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 `const 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`.
 
 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.
 
@@ -86,7 +86,7 @@ assert(
 
 ```js
 // The global variable
-var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];
+const bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];
 
 // Change code below this line
 function add (bookName) {
@@ -99,7 +99,7 @@ function add (bookName) {
 
 // Change code below this line
 function remove (bookName) {
-  var book_index = bookList.indexOf(bookName);
+  const book_index = bookList.indexOf(bookName);
   if (book_index >= 0) {
 
     bookList.splice(book_index, 1);
@@ -109,9 +109,9 @@ function remove (bookName) {
     }
 }
 
-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');
+const newBookList = add(bookList, 'A Brief History of Time');
+const newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
+const newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');
 
 console.log(bookList);
 ```
@@ -120,13 +120,13 @@ console.log(bookList);
 
 ```js
 // The global variable
-var bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];
+const bookList = ["The Hound of the Baskervilles", "On The Electrodynamics of Moving Bodies", "Philosophiæ Naturalis Principia Mathematica", "Disquisitiones Arithmeticae"];
 
-function add (bookList, bookName) {
+function add(bookList, bookName) {
   return [...bookList, bookName];
 }
 
-function remove (bookList, bookName) {
+function remove(bookList, bookName) {
   const bookListCopy = [...bookList];
   const bookNameIndex = bookList.indexOf(bookName);
   if (bookNameIndex >= 0) {
@@ -135,7 +135,7 @@ function remove (bookList, bookName) {
   return bookListCopy;
 }
 
-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');
+const newBookList = add(bookList, 'A Brief History of Time');
+const newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
+const newestBookList = remove(add(bookList, 'A Brief History of Time'), 'On The Electrodynamics of Moving Bodies');
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/remove-elements-from-an-array-using-slice-instead-of-splice.md

@@ -11,7 +11,7 @@ dashedName: remove-elements-from-an-array-using-slice-instead-of-splice
 A common pattern while working with arrays is when you want to remove items and keep the rest of the array. JavaScript offers the `splice` 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 `splice` method mutates the original array it is called on. Here's an example:
 
 ```js
-var cities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
+const cities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
 cities.splice(3, 1);
 ```
 
@@ -69,7 +69,8 @@ function nonMutatingSplice(cities) {
 
   // Only change code above this line
 }
-var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
+
+const inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
 nonMutatingSplice(inputCities);
 ```
 
@@ -77,10 +78,7 @@ nonMutatingSplice(inputCities);
 
 ```js
 function nonMutatingSplice(cities) {
-  // Only change code below this line
   return cities.slice(0,3);
-  // Only change code above this line
 }
-var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
-nonMutatingSplice(inputCities);
+const inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/return-a-sorted-array-without-changing-the-original-array.md

@@ -68,24 +68,23 @@ assert(JSON.stringify(nonMutatingSort([140000, 104, 99])) ===
 ## --seed-contents--
 
 ```js
-var globalArray = [5, 6, 3, 2, 9];
+const globalArray = [5, 6, 3, 2, 9];
+
 function nonMutatingSort(arr) {
   // Only change code below this line
 
 
   // Only change code above this line
 }
+
 nonMutatingSort(globalArray);
 ```
 
 # --solutions--
 
 ```js
-var globalArray = [5, 6, 3, 2, 9];
+const globalArray = [5, 6, 3, 2, 9];
 function nonMutatingSort(arr) {
-  // Only change code below this line
   return [].concat(arr).sort((a,b) => a-b);
-  // Only change code above this line
 }
-nonMutatingSort(globalArray);
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/return-part-of-an-array-using-the-slice-method.md

@@ -13,8 +13,8 @@ The `slice` method returns a copy of certain elements of an array. It can take t
 Here's an example:
 
 ```js
-var arr = ["Cat", "Dog", "Tiger", "Zebra"];
-var newArray = arr.slice(1, 3);
+const arr = ["Cat", "Dog", "Tiger", "Zebra"];
+const newArray = arr.slice(1, 3);
 ```
 
 `newArray` would have the value `["Dog", "Tiger"]`.
@@ -78,7 +78,8 @@ function sliceArray(anim, beginSlice, endSlice) {
 
   // Only change code above this line
 }
-var inputAnim = ["Cat", "Dog", "Tiger", "Zebra", "Ant"];
+
+const inputAnim = ["Cat", "Dog", "Tiger", "Zebra", "Ant"];
 sliceArray(inputAnim, 1, 3);
 ```
 
@@ -86,10 +87,7 @@ sliceArray(inputAnim, 1, 3);
 
 ```js
 function sliceArray(anim, beginSlice, endSlice) {
-  // Only change code below this line
-  return anim.slice(beginSlice, endSlice)
-  // Only change code above this line
+  return anim.slice(beginSlice, endSlice);
 }
-var inputAnim = ["Cat", "Dog", "Tiger", "Zebra", "Ant"];
-sliceArray(inputAnim, 1, 3);
+const inputAnim = ["Cat", "Dog", "Tiger", "Zebra", "Ant"];
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/sort-an-array-alphabetically-using-the-sort-method.md

@@ -18,6 +18,7 @@ function ascendingOrder(arr) {
     return a - b;
   });
 }
+
 ascendingOrder([1, 5, 2, 3, 4]);
 ```
 
@@ -29,6 +30,7 @@ function reverseAlpha(arr) {
     return a === b ? 0 : a < b ? 1 : -1;
   });
 }
+
 reverseAlpha(['l', 'h', 'z', 'b', 's']);
 ```
 
@@ -86,6 +88,7 @@ function alphabeticalOrder(arr) {
   return arr
   // Only change code above this line
 }
+
 alphabeticalOrder(["a", "d", "c", "a", "z", "g"]);
 ```
 
@@ -93,9 +96,6 @@ alphabeticalOrder(["a", "d", "c", "a", "z", "g"]);
 
 ```js
 function alphabeticalOrder(arr) {
-  // Only change code below this line
   return arr.sort();
-  // Only change code above this line
 }
-alphabeticalOrder(["a", "d", "c", "a", "z", "g"]);
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/split-a-string-into-an-array-using-the-split-method.md

@@ -13,11 +13,11 @@ The `split` method splits a string into an array of strings. It takes an argumen
 Here are two examples that split one string by spaces, then another by digits using a regular expression:
 
 ```js
-var str = "Hello World";
-var bySpace = str.split(" ");
+const str = "Hello World";
+const bySpace = str.split(" ");
 
-var otherString = "How9are7you2today";
-var byDigits = otherString.split(/\d/);
+const otherString = "How9are7you2today";
+const byDigits = otherString.split(/\d/);
 ```
 
 `bySpace` would have the value `["Hello", "World"]` and `byDigits` would have the value `["How", "are", "you", "today"]`.
@@ -74,6 +74,7 @@ function splitify(str) {
 
   // Only change code above this line
 }
+
 splitify("Hello World,I-am code");
 ```
 
@@ -81,8 +82,6 @@ splitify("Hello World,I-am code");
 
 ```js
 function splitify(str) {
-  // Only change code below this line
   return str.split(/\W/);
-  // Only change code above this line
 }
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/understand-the-hazards-of-using-imperative-code.md

@@ -59,29 +59,29 @@ assert.deepEqual(finalTabs.tabs, [
 
 ```js
 // tabs is an array of titles of each site open within the window
-var Window = function(tabs) {
+const Window = function(tabs) {
   this.tabs = tabs; // We keep a record of the array inside the object
 };
 
 // When you join two windows into one window
-Window.prototype.join = function (otherWindow) {
+Window.prototype.join = function(otherWindow) {
   this.tabs = this.tabs.concat(otherWindow.tabs);
   return this;
 };
 
 // When you open a new tab at the end
-Window.prototype.tabOpen = function (tab) {
+Window.prototype.tabOpen = function(tab) {
   this.tabs.push('new tab'); // Let's open a new tab for now
   return this;
 };
 
 // When you close a tab
-Window.prototype.tabClose = function (index) {
+Window.prototype.tabClose = function(index) {
 
   // Only change code below this line
 
-  var tabsBeforeIndex = this.tabs.splice(0, index); // Get the tabs before the tab
-  var tabsAfterIndex = this.tabs.splice(index + 1); // Get the tabs after the tab
+  const tabsBeforeIndex = this.tabs.splice(0, index); // Get the tabs before the tab
+  const tabsAfterIndex = this.tabs.splice(index + 1); // Get the tabs after the tab
 
   this.tabs = tabsBeforeIndex.concat(tabsAfterIndex); // Join them together
 
@@ -91,12 +91,12 @@ Window.prototype.tabClose = function (index) {
  };
 
 // Let's create three browser windows
-var workWindow = new Window(['GMail', 'Inbox', 'Work mail', 'Docs', 'freeCodeCamp']); // Your mailbox, drive, and other work sites
-var socialWindow = new Window(['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium']); // Social sites
-var videoWindow = new Window(['Netflix', 'YouTube', 'Vimeo', 'Vine']); // Entertainment sites
+const workWindow = new Window(['GMail', 'Inbox', 'Work mail', 'Docs', 'freeCodeCamp']); // Your mailbox, drive, and other work sites
+const socialWindow = new Window(['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium']); // Social sites
+const videoWindow = new Window(['Netflix', 'YouTube', 'Vimeo', 'Vine']); // Entertainment sites
 
 // Now perform the tab opening, closing, and other operations
-var finalTabs = socialWindow
+const finalTabs = socialWindow
   .tabOpen() // Open a new tab for cat memes
   .join(videoWindow.tabClose(2)) // Close third tab in video window, and join
   .join(workWindow.tabClose(1).tabOpen());
@@ -106,40 +106,34 @@ console.log(finalTabs.tabs);
 # --solutions--
 
 ```js
-// tabs is an array of titles of each site open within the window
-var Window = function(tabs) {
-  this.tabs = tabs; // We keep a record of the array inside the object
+const Window = function(tabs) {
+  this.tabs = tabs;
 };
 
-// When you join two windows into one window
-Window.prototype.join = function (otherWindow) {
+Window.prototype.join = function(otherWindow) {
   this.tabs = this.tabs.concat(otherWindow.tabs);
   return this;
 };
 
-// When you open a new tab at the end
-Window.prototype.tabOpen = function (tab) {
-  this.tabs.push('new tab'); // Let's open a new tab for now
+Window.prototype.tabOpen = function(tab) {
+  this.tabs.push('new tab');
   return this;
 };
 
-// When you close a tab
-Window.prototype.tabClose = function (index) {
-  var tabsBeforeIndex = this.tabs.slice(0, index); // Get the tabs before the tab
-  var tabsAfterIndex = this.tabs.slice(index + 1); // Get the tabs after the tab
+Window.prototype.tabClose = function(index) {
+  const tabsBeforeIndex = this.tabs.slice(0, index);
+  const tabsAfterIndex = this.tabs.slice(index + 1);
 
-  this.tabs = tabsBeforeIndex.concat(tabsAfterIndex); // Join them together
+  this.tabs = tabsBeforeIndex.concat(tabsAfterIndex);
   return this;
  };
 
-// Let's create three browser windows
-var workWindow = new Window(['GMail', 'Inbox', 'Work mail', 'Docs', 'freeCodeCamp']); // Your mailbox, drive, and other work sites
-var socialWindow = new Window(['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium']); // Social sites
-var videoWindow = new Window(['Netflix', 'YouTube', 'Vimeo', 'Vine']); //  Entertainment sites
+const workWindow = new Window(['GMail', 'Inbox', 'Work mail', 'Docs', 'freeCodeCamp']);
+const socialWindow = new Window(['FB', 'Gitter', 'Reddit', 'Twitter', 'Medium']);
+const videoWindow = new Window(['Netflix', 'YouTube', 'Vimeo', 'Vine']);
 
-// Now perform the tab opening, closing, and other operations
-var finalTabs = socialWindow
-  .tabOpen() // Open a new tab for cat memes
-  .join(videoWindow.tabClose(2)) // Close third tab in video window, and join
+const finalTabs = socialWindow
+  .tabOpen()
+  .join(videoWindow.tabClose(2))
   .join(workWindow.tabClose(1).tabOpen());
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/use-the-every-method-to-check-that-every-element-in-an-array-meets-a-criteria.md

@@ -13,7 +13,8 @@ The `every` method works with arrays to check if *every* element passes a partic
 For example, the following code would check if every element in the `numbers` array is less than 10:
 
 ```js
-var numbers = [1, 5, 8, 0, 10, 11];
+const numbers = [1, 5, 8, 0, 10, 11];
+
 numbers.every(function(currentValue) {
   return currentValue < 10;
 });
@@ -62,6 +63,7 @@ function checkPositive(arr) {
 
   // Only change code above this line
 }
+
 checkPositive([1, 2, 3, -4, 5]);
 ```
 
@@ -69,9 +71,6 @@ checkPositive([1, 2, 3, -4, 5]);
 
 ```js
 function checkPositive(arr) {
-  // Only change code below this line
   return arr.every(num => num > 0);
-  // Only change code above this line
 }
-checkPositive([1, 2, 3, -4, 5]);
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/use-the-filter-method-to-extract-data-from-an-array.md

@@ -55,7 +55,7 @@ Your code should not use a `for` loop.
 assert(!code.match(/for\s*?\([\s\S]*?\)/g));
 ```
 
-`filteredList` should equal `[{"title": "Inception","rating": "8.8"},{"title": "Interstellar","rating": "8.6"},{"title": "The Dark Knight","rating": "9.0"},{"title": "Batman Begins","rating": "8.3"}]`.
+`filteredList` should equal `[{"title": "Inception", "rating": "8.8"}, {"title": "Interstellar", "rating": "8.6"}, {"title": "The Dark Knight", "rating": "9.0"}, {"title": "Batman Begins", "rating": "8.3"}]`.
 
 ```js
 assert.deepEqual(filteredList, [
@@ -72,7 +72,7 @@ assert.deepEqual(filteredList, [
 
 ```js
 // The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -187,7 +187,7 @@ var watchList = [
 
 // Only change code below this line
 
-var filteredList;
+const filteredList = "";
 
 // Only change code above this line
 
@@ -197,8 +197,7 @@ console.log(filteredList);
 # --solutions--
 
 ```js
-// The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -311,7 +310,5 @@ var watchList = [
   }
 ];
 
-// Only change code below this line
-let filteredList = watchList.filter(e => e.imdbRating >= 8).map( ({Title: title, imdbRating: rating}) => ({title, rating}) );
-// Only change code above this line
+const filteredList = watchList.filter(e => e.imdbRating >= 8).map( ({Title: title, imdbRating: rating}) => ({title, rating}) );
 ```

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/use-the-map-method-to-extract-data-from-an-array.md

@@ -61,7 +61,7 @@ Your code should use the `map` method.
 assert(code.match(/\.map/g));
 ```
 
-`ratings` should equal `[{"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"}]`.
+`ratings` should equal `[{"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"}]`.
 
 ```js
 assert.deepEqual(ratings, [
@@ -79,7 +79,7 @@ assert.deepEqual(ratings, [
 
 ```js
 // The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -194,9 +194,9 @@ var watchList = [
 
 // Only change code below this line
 
-var ratings = [];
-for(var i=0; i < watchList.length; i++){
-  ratings.push({title: watchList[i]["Title"],  rating: watchList[i]["imdbRating"]});
+const ratings = [];
+for (let i = 0; i < watchList.length; i++) {
+  ratings.push({title: watchList[i]["Title"], rating: watchList[i]["imdbRating"]});
 }
 
 // Only change code above this line
@@ -207,8 +207,7 @@ console.log(JSON.stringify(ratings));
 # --solutions--
 
 ```js
-// The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -321,7 +320,7 @@ var watchList = [
   }
 ];
 
-var ratings = watchList.map(function(movie) {
+const ratings = watchList.map(function(movie) {
   return {
     title: movie["Title"],
     rating: movie["imdbRating"]

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/use-the-reduce-method-to-analyze-data.md

@@ -93,7 +93,7 @@ assert(getRating(watchList.filter((_, i) => i < 1 || i > 2)) === 8.55);
 
 ```js
 // The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -206,22 +206,22 @@ var watchList = [
   }
 ];
 
-function getRating(watchList){
+function getRating(watchList) {
   // Only change code below this line
-  var averageRating;
+  let averageRating;
 
 
   // Only change code above this line
   return averageRating;
 }
+
 console.log(getRating(watchList));
 ```
 
 # --solutions--
 
 ```js
-// The global variable
-var watchList = [
+const watchList = [
   {
     "Title": "Inception",
     "Year": "2010",
@@ -334,8 +334,8 @@ var watchList = [
   }
 ];
 
-function getRating(watchList){
-  var averageRating;
+function getRating(watchList) {
+  let averageRating;
   const rating = watchList
     .filter(obj => obj.Director === "Christopher Nolan")
     .map(obj => Number(obj.imdbRating));

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/use-the-some-method-to-check-that-any-elements-in-an-array-meet-a-criteria.md

@@ -13,7 +13,8 @@ The `some` method works with arrays to check if *any* element passes a particula
 For example, the following code would check if any element in the `numbers` array is less than 10:
 
 ```js
-var numbers = [10, 50, 8, 220, 110, 11];
+const numbers = [10, 50, 8, 220, 110, 11];
+
 numbers.some(function(currentValue) {
   return currentValue < 10;
 });
@@ -62,6 +63,7 @@ function checkPositive(arr) {
 
   // Only change code above this line
 }
+
 checkPositive([1, 2, 3, -4, 5]);
 ```
 
@@ -69,9 +71,6 @@ checkPositive([1, 2, 3, -4, 5]);
 
 ```js
 function checkPositive(arr) {
-  // Only change code below this line
   return arr.some(elem => elem > 0);
-  // Only change code above this line
 }
-checkPositive([1, 2, 3, -4, 5]);
 ```