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>
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@ -8,6 +8,8 @@ dashedName: compare-scopes-of-the-var-and-let-keywords
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# --description--
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If you are unfamiliar with `let`, check out [this challenge](/learn/javascript-algorithms-and-data-structures/basic-javascript/explore-differences-between-the-var-and-let-keywords).
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When you declare a variable with the `var` keyword, it is declared globally, or locally if declared inside a function.
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The `let` keyword behaves similarly, but with some extra features. When you declare a variable with the `let` keyword inside a block, statement, or expression, its scope is limited to that block, statement, or expression.
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@ -1,89 +0,0 @@
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---
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id: 587d7b87367417b2b2512b41
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title: Declare a Read-Only Variable with the const Keyword
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challengeType: 1
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forumTopicId: 301201
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dashedName: declare-a-read-only-variable-with-the-const-keyword
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---
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# --description--
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The keyword `let` is not the only new way to declare variables. In ES6, you can also declare variables using the `const` keyword.
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`const` has all the awesome features that `let` has, with the added bonus that variables declared using `const` are read-only. They are a constant value, which means that once a variable is assigned with `const`, it cannot be reassigned.
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```js
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const FAV_PET = "Cats";
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FAV_PET = "Dogs";
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```
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The console will display an error due to reassigning the value of `FAV_PET`.
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As you can see, trying to reassign a variable declared with `const` will throw an error. You should always name variables you don't want to reassign using the `const` keyword. This helps when you accidentally attempt to reassign a variable that is meant to stay constant. A common practice when naming constants is to use all uppercase letters, with words separated by an underscore.
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**Note:** It is common for developers to use uppercase variable identifiers for immutable values and lowercase or camelCase for mutable values (objects and arrays). In a later challenge you will see an example of a lowercase variable identifier being used for an array.
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# --instructions--
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Change the code so that all variables are declared using `let` or `const`. Use `let` when you want the variable to change, and `const` when you want the variable to remain constant. Also, rename variables declared with `const` to conform to common practices, meaning constants should be in all caps.
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# --hints--
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`var` should not exist in your code.
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```js
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(getUserInput) => assert(!getUserInput('index').match(/var/g));
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```
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`SENTENCE` should be a constant variable declared with `const`.
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```js
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(getUserInput) => assert(getUserInput('index').match(/(const SENTENCE)/g));
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```
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`i` should be declared with `let`.
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```js
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(getUserInput) => assert(getUserInput('index').match(/(let i)/g));
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```
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`console.log` should be changed to print the `SENTENCE` variable.
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```js
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(getUserInput) =>
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assert(getUserInput('index').match(/console\.log\(\s*SENTENCE\s*\)\s*;?/g));
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```
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# --seed--
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## --seed-contents--
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```js
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function printManyTimes(str) {
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// Only change code below this line
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var sentence = str + " is cool!";
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for (var i = 0; i < str.length; i+=2) {
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console.log(sentence);
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}
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// Only change code above this line
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}
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printManyTimes("freeCodeCamp");
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```
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# --solutions--
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```js
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function printManyTimes(str) {
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const SENTENCE = str + " is cool!";
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for (let i = 0; i < str.length; i+=2) {
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console.log(SENTENCE);
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}
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}
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printManyTimes("freeCodeCamp");
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```
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@ -1,91 +0,0 @@
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---
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id: 587d7b87367417b2b2512b3f
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title: Explore Differences Between the var and let Keywords
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challengeType: 1
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forumTopicId: 301202
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dashedName: explore-differences-between-the-var-and-let-keywords
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---
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# --description--
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One of the biggest problems with declaring variables with the `var` keyword is that you can overwrite variable declarations without an error.
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```js
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var camper = 'James';
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var camper = 'David';
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console.log(camper);
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```
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Here the console will display the string `David`.
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As you can see in the code above, the `camper` variable is originally declared as `James` and then overridden to be `David`. In a small application, you might not run into this type of problem, but when your code becomes larger, you might accidentally overwrite a variable that you did not intend to overwrite. Because this behavior does not throw an error, searching and fixing bugs becomes more difficult.
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A new keyword called `let` was introduced in ES6 to solve this potential issue with the `var` keyword. If you were to replace `var` with `let` in the variable declarations of the code above, the result would be an error.
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```js
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let camper = 'James';
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let camper = 'David';
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```
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This error can be seen in the console of your browser. So unlike `var`, when using `let`, a variable with the same name can only be declared once. Note the `"use strict"`. This enables Strict Mode, which catches common coding mistakes and "unsafe" actions. For instance:
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```js
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"use strict";
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x = 3.14;
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```
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This will display an error that `x is not defined`.
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# --instructions--
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Update the code so it only uses the `let` keyword.
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# --hints--
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`var` should not exist in the code.
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```js
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(getUserInput) => assert(!getUserInput('index').match(/var/g));
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```
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`catName` should be the string `Oliver`.
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```js
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assert(catName === 'Oliver');
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```
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`quote` should be the string `Oliver says Meow!`
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```js
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assert(quote === 'Oliver says Meow!');
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```
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# --seed--
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## --seed-contents--
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```js
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var catName;
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var quote;
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function catTalk() {
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"use strict";
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catName = "Oliver";
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quote = catName + " says Meow!";
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}
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catTalk();
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```
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# --solutions--
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```js
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let catName;
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let quote;
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function catTalk() {
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'use strict';
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catName = 'Oliver';
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quote = catName + ' says Meow!';
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}
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catTalk();
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```
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@ -8,6 +8,8 @@ dashedName: mutate-an-array-declared-with-const
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# --description--
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If you are unfamiliar with `const`, check out [this challenge](/learn/javascript-algorithms-and-data-structures/basic-javascript/declare-a-read-only-variable-with-the-const-keyword).
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The `const` declaration has many use cases in modern JavaScript.
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Some developers prefer to assign all their variables using `const` by default, unless they know they will need to reassign the value. Only in that case, they use `let`.
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