88 lines
2.6 KiB
Markdown
88 lines
2.6 KiB
Markdown
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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"; // returns error
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```
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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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