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

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
587d7b87367417b2b2512b41	Declare a Read-Only Variable with the const Keyword	1	301201	declare-a-read-only-variable-with-the-const-keyword

--description--

The keyword let is not the only new way to declare variables. In ES6, you can also declare variables using the const keyword.

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:

const FAV_PET = "Cats";
FAV_PET = "Dogs";

The console will display an error due to reassigning the value of FAV_PET.

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.

Note: It is common for developers to use uppercase variable identifiers for immutable values and lowercase or camelCase for mutable values (objects and arrays). You will learn more about objects, arrays, and immutable and mutable values in later challenges. Also in later challenges, you will see examples of uppercase, lowercase, or camelCase variable identifiers.

--instructions--

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.

--hints--

var should not exist in your code.

(getUserInput) => assert(!getUserInput('index').match(/var/g));

You should change fCC to all uppercase.

(getUserInput) => {
  assert(getUserInput('index').match(/(FCC)/));
  assert(!getUserInput('index').match(/fCC/));
}

FCC should be a constant variable declared with const.

assert.equal(FCC, 'freeCodeCamp');
assert.match(code, /const\s+FCC/);

fact should be declared with let.

(getUserInput) => assert(getUserInput('index').match(/(let fact)/g));

console.log should be changed to print the FCC and fact variables.

(getUserInput) =>
  assert(getUserInput('index').match(/console\.log\(\s*FCC\s*\,\s*fact\s*\)\s*;?/g));

--seed--

--seed-contents--

// Only change code below this line
var fCC = "freeCodeCamp";
var fact = "is cool!";
// Only change code above this line

fact = "is awesome!";
console.log(fCC, fact);

--solutions--

const FCC = "freeCodeCamp";
let fact = "is cool!";

fact = "is awesome!";
console.log(FCC, fact);