freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/es6/explore-differences-between-the-var-and-let-keywords.md

---
id: 587d7b87367417b2b2512b3f
title: Explore Differences Between the var and let Keywords
challengeType: 1
forumTopicId: 301202
---

## Description
<section id='description'>
One of the biggest problems with declaring variables with the <code>var</code> keyword is that you can overwrite variable declarations without an error.

```js
var camper = 'James';
var camper = 'David';
console.log(camper);
// logs 'David'
```

As you can see in the code above, the <code>camper</code> variable is originally declared as <code>James</code> and then overridden to be <code>David</code>.
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.<br>
A new keyword called <code>let</code> was introduced in ES6 to solve this potential issue with the <code>var</code> keyword.
If you were to replace <code>var</code> with <code>let</code> in the variable declarations of the code above, the result would be an error.

```js
let camper = 'James';
let camper = 'David'; // throws an error
```

This error can be seen in the console of your browser.
So unlike <code>var</code>, when using <code>let</code>, a variable with the same name can only be declared once.
Note the <code>"use strict"</code>. This enables Strict Mode, which catches common coding mistakes and "unsafe" actions. For instance:

```js
"use strict";
x = 3.14; // throws an error because x is not declared
```

</section>

## Instructions
<section id='instructions'>
Update the code so it only uses the <code>let</code> keyword.
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>var</code> should not exist in the code.
    testString: getUserInput => assert(!getUserInput('index').match(/var/g));
  - text: <code>catName</code> should be <code>Oliver</code>.
    testString: assert(catName === "Oliver");
  - text: <code>quote</code> should be <code>"Oliver says Meow!"</code>
    testString: assert(quote === "Oliver says Meow!");

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
var catName;
var quote;
function catTalk() {
  "use strict";

  catName = "Oliver";
  quote = catName + " says Meow!";

}
catTalk();
```

</div>



</section>

## Solution
<section id='solution'>

```js
let catName;
let quote;
function catTalk() {
  'use strict';

  catName = 'Oliver';
  quote = catName + ' says Meow!';
}
catTalk();
```

</section>