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How to work on coding challenges

Our goal is to develop a fun and clear interactive learning experience.

Designing interactive coding challenges is difficult. It would be much easier to write a lengthy explanation or to create a video tutorial. But for our core curriculum, we're sticking with what works best for most people - a fully interactive, video game-like experience.

We want campers to achieve a flow state. We want them to build momentum and blast through our curriculum with as few snags as possible. We want them to go into the projects with confidence and gain a wide exposure to programming concepts.

Note that for Version 7.0 of the freeCodeCamp curriculum, we are moving toward an entirely project-focused model with a lot more repetition.

Creating these challenges requires immense creativity and attention to detail. There's plenty of help available. You'll have support from a whole team of contributors to whom you can bounce ideas off and demo your challenges.

And as always, feel free to ask questions on the 'Contributors' category on our forum or the contributors chat room.

With your help, we can design an interactive coding curriculum that will help millions of people learn to code for years to come.

The content for each challenge is stored in its markdown file. This markdown file is later converted to HTML using our tools to create interactive web pages.

You can find all of freeCodeCamp.org's curricular content in the /curriculum/challenges directory.

Set up the tooling for the curriculum

Before you work on the curriculum, you would need to set up some tooling to help you test your changes. You can use any option from the below:

You can set up freeCodeCamp locally. This is highly recommended for regular/repeat contributions. This setup allows you to work and test your changes.
Use Gitpod, a free online dev environment. Clicking the button below will start a ready-to-code dev environment for freeCodeCamp in your browser. It only takes a few minutes.
Edit the files on GitHub's interface by clicking the pencil icon for the corresponding file. While this is the quickest way, It is not recommended, because you are unable to test your changes on GitHub. If our maintainers conclude that the changes you made need to be tested locally, you would need to follow the methods above instead.

How to work on practice projects

The practice projects have some additional tooling to help create new projects and steps. To read more, see these docs

Challenge Template

---
id: Unique identifier (alphanumerical, MongoDB_id)
title: 'Challenge Title'
challengeType: Integer, defined in `client/utils/challengeTypes.js`
videoUrl: 'url of video explanation'
forumTopicId: 12345
---

# --description--

Challenge description text, in markdown

```html
<div>example code</div>
```

# --instructions--

Challenge instruction text, in markdown

# --hints--

Tests to run against user code, in pairs of markdown text and code block test code.

```js
Code for test one
```

More instructions in markdown syntax

```js
More code
```

# --seed--

## --before-user-code--

```lang
Code evaluated before the user’s code.
```

## --after-user-code--

```lang
Code evaluated after the user’s code, and just before the tests
```

## --seed-contents--

Boilerplate code to render to the editor. This section should only contain code inside backticks, like the following:

```html
<body>
  <p class="main-text">Hello world!</p>
</body>
```

```css
body {
  margin: 0;
  background-color: #3a3240;
}

.main-text {
  color: #aea8d3;
}
```

```js
console.log('freeCodeCamp is awesome!');
```

# --solutions--

Solutions are used for the CI tests to ensure that changes to the hints will still pass as intended

```js
// first solution - the language(s) should match the seed.
```

---

```js
// second solution - so if the seed is written in HTML...
```

---

```js
// third solution etc. - Your solutions should be in HTML.
```

# --question--

These fields are currently used for the multiple-choice Python challenges.

## --text--

The question text goes here.

## --answers--

Answer 1

---

Answer 2

---

More answers

## --video-solution--

The number for the correct answer goes here.

[!NOTE]

In the above sections, examples of lang are:

html - HTML/CSS

js - JavaScript

jsx - JSX

Numbering Challenges

Every challenge needs an id. If you don't specify one, then MongoDB will create a new random one when it saves the data; however, we don't want it to do that, since we want the challenge ids to be consistent across different environments (staging, production, lots of different developers, etc.).

To generate a new one in a shell (assuming MongoDB is running separately):

Run mongo command.
Run ObjectId() command.

For example:

$ mongo
MongoDB shell version v3.6.1
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.10
...
$ ObjectId()
ObjectId("5a474d78df58bafeb3535d34")

The result is a new id, for example 5a474d78df58bafeb3535d34 above.

Once you have your id, put it into the markdown file as the id field at the top, e.g.

---
id: 5a474d78df58bafeb3535d34
title: Challenge Title

Naming challenges

Naming things is hard. We've made it easier by imposing some constraints.

All challenge titles should be explicit and should follow this pattern:

[verb][object clause]

Here are some example challenge names:

Use Clockwise Notation to Specify the Padding of an Element
Condense arrays with .reduce
Use Bracket Notation to Find the First Character in a String

Challenge descriptions/instructions

Sentences should be clear and concise with minimal jargon. If used, jargon should be immediately defined in plain English.

Keep paragraphs short (around 1-4 sentences). People are more likely to read several short paragraphs than a wall of text.

Challenge text should use the second person ("you") to help to give it a conversational tone. This way the text and instructions seem to speak directly to the camper working through the challenge. Try to avoid using the first person ("I", "we", "let's", and "us").

Don't use outbound links. These interrupt the flow. Campers should never have to google anything during these challenges. If there are resources you think campers would benefit from, add them to the challenge's Guide-related article.

You can add diagrams if necessary.

Don't use emojis or emoticons in challenges. freeCodeCamp has a global community, and the cultural meaning of an emoji or emoticon may be different around the world. Also, emojis can render differently on different systems.

Proper nouns should use correct capitalization when possible. Below is a list of words as they should appear in the challenges.

JavaScript (capital letters in "J" and "S" and no abbreviations)
Node.js
Although sometimes inaccurate, non-hyphenated forms of 'back end' and 'front end' should be used, as they are more widely used.

The 2-minute rule

Each challenge should be solvable within 120 seconds by a native English speaker who has completed the challenges leading up to it. This includes the amount of time it takes to read the directions/instructions understand the seeded code, write their code and get all the tests to pass.

If it takes longer than two minutes to complete the challenge, you have two options:

Simplify the challenge, or
Split the challenge into two challenges.

The 2-minute rule forces you, the challenge designer, to make your directions concise, your seed code clear, and your tests straight-forward.

We track how long it takes for campers to solve changes and use this information to identify challenges that need to be simplified or split.

Modularity

Each challenge should teach exactly one concept, and that concept should be apparent from the challenge's name.

We can reinforce previously covered concepts through repetition and variations - for example, introducing h1 elements in one challenge, then h3 elements a few challenges later.

Our goal is to have thousands of 2-minute challenges. These can flow together and reiterate previously-covered concepts.

Formatting challenge text

Here are specific formatting guidelines for challenge text and examples:

Language keywords go in ``` backticks. For example, HTML tag names or CSS property names.
References to code parts (i.e. function, method, or variable names) should be wrapped in ``` backticks. See example below:

Use `parseInt` to convert the variable `realNumber` into an integer.

References to file names and path directories (e.g. package.json, src/components) should be wrapped in ``` backticks.
Multi-line code blocks must be preceded by an empty line. The next line must start with three backticks followed immediately by one of the supported languages. To complete the code block, you must start a new line which only has three backticks and another empty line. See example below:
Whitespace matters in Markdown, so we recommend that you make it visible in your editor.

Note: If you are going to use an example code in YAML, use yaml instead of yml for the language to the right of the backticks.

The following is an example of code:

```{language}

[YOUR CODE HERE]

```

Additional information in the form of a note should be surrounded by blank lines, and formatted: **Note:** Rest of note text...
If multiple notes are needed, then list all of the notes in separate sentences using the format: **Notes:** First note text. Second note text.
Use single-quotes where applicable

Note: The equivalent Markdown should be used in place of HTML tags.

Writing tests

Challenges should have the minimum number of tests necessary to verify that a camper understands a concept.

Our goal is to communicate the single point that the challenge is trying to teach, and test that they have understood that point.

Challenge tests can make use of the Node.js and Chai.js assertion libraries. Also, if needed, user-generated code can be accessed in the code variable. In addition, the __helpers object exposes several functions that simplify the process of writing tests. The available functions are defined in client/src/utils/curriculum-helpers.ts.

Formatting seed code

Here are specific formatting guidelines for the challenge seed code:

Use two spaces to indent
JavaScript statements end with a semicolon
Use double quotes where applicable

Seed code comments

We have a comment dictionary that contains the only comments that can be used within the seed code. The exact case and spacing of the dictionary comment must be used. The comment dictionary should not be expanded without prior discussion with the dev-team.

Comments used should have a space between the comment characters and the comment themselves. In general, comments should be used sparingly. Always consider rewriting a challenge's description or instructions if it could avoid using a seed code comment.

Example of valid single line JavaScript comment:

// Only change code below this line

Example of a valid CSS comment:

/* Only change code above this line */

If a challenge only has a single place where code changes are needed, please use the comments in the following example to instruct the user where changes should be made.

var a = 3;
var b = 17;
var c = 12;

// Only change code below this line
a = a + 12;
b = 9 + b;
c = c + 7;

If a challenge has multiple places where the user is expected to change code (i.e. the React challenges)

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      text: 'Hello'
    };
    // Change code below this line

    // Change code above this line
  }
  handleClick() {
    this.setState({
      text: 'You clicked!'
    });
  }
  render() {
    return (
      <div>
        {/* Change code below this line */}
        <button>Click Me</button>
        {/* Change code above this line */}
        <h1>{this.state.text}</h1>
      </div>
    );
  }
}

Translation of seed code comments

There are separate comment dictionaries for each language. The English version of the comment dictionary is the basis for the translations found in the corresponding non-English versions of the files. The non-English version of the Chinese comment dictionary would be located at /curriculum/dictionaries/chinese/comments.js. Each dictionary consists of an array of objects with a unique id property and a text property. Only the text should be modified to encompass the translation of the corresponding English comment.

Some comments may contain a word/phrase that should not be translated. For example, variable names or proper library names like "React" should not be translated. See the comment below as an example. The word myGlobal should not be translated.

Declare the myGlobal variable below this line

[!NOTE]

We are working on an integration to make it possible to work on i18n for the comment dictionary.

Hints and Solutions

Each challenge has a Get a Hint button, so a user can access any hints/solutions which have been created for the challenge. Curriculum hints/solutions topics are located on our forum under the Guide category.

If you find a problem with an existing challenge's hints/solutions topic, you can make suggestions in the contributors category on the forum. Moderators and users with trust level 3 will review the comments and decide whether or not to include the changes in the corresponding hint/solutions topic.

Adding new Challenge hints/solutions Topics

Take the following steps when adding a new challenge hints/solutions related topic.

Start by following the same steps for creating a new topic but review the next for creating the title.
The title of the topic should start with freeCodeCamp Challenge Guide: concatenated with the actual title of the curriculum challenge. For example, if the challenge is named "Chunky Monkey", the topic title would be "freeCodeCamp Challenge Guide: Chunky Monkey".
camperbot should be the owner of these topics/posts, so you will need to request an admin to change the ownership of the main post to camperbot.
Once the new topic is created, a forum topic id is created. It is located at the end of the forum topic URL. This id must be added to the frontmatter of the curriculum challenge file via the normal pull request process for the Get a Hint button to link to the topic.

Guidelines for content of hints and solutions topics

When proposing a solution for a curriculum challenge related Guide topic, the full code must be added. This includes all the original seed code plus any changes needed to pass all the challenge tests. The following template should be used when creating new hints/solutions topics:

# Challenge Name Goes Here

---

## Problem Explanation

This summarizes what needs to be done without just restating the challenge description and/or instructions. This is an optional section

#### Relevant Links

- [Link Text](link_url_goes_here)
- [Link Text](link_url_goes_here)

---

## Hints

### Hint 1

Hint goes here

### Hint 2

Hint goes here

---

## Solutions

<details><summary>Solution 1 (Click to Show/Hide)</summary>

```js
function myFunc() {
  console.log('Hello World!');
}
```

#### Code Explanation

- Code explanation goes here
- Code explanation goes here

#### Relevant Links

- [Link Text](link_url_goes_here)
- [Link Text](link_url_goes_here)

</details>

Testing Challenges

Before you create a pull request for your changes, you need to validate that the changes you have made do not inadvertently cause problems with the challenge.

To test all challenges run the below command from the root directory

npm run test:curriculum

You can also test a block or a superblock of challenges with these commands

npm run test:curriculum --block='Basic HTML and HTML5'

npm run test:curriculum --superblock=responsive-web-design

You are also able to test one challenge individually by performing the following steps:

Switch to the curriculum directory:
```
cd curriculum
```
Run the following for each challenge file for which you have changed (replacing challenge-title-goes-here with the full title of the challenge):
```
npm run test -- -g challenge-title-goes-here
```

Once you have verified that each challenge you've worked on passes the tests, please create a pull request.

[!TIP] You can set the environment variable LOCALE in the .env to the language of the challenge(s) you need to test.

The currently accepted values are english and chinese, with english being set by default.

Useful Links

Creating and Editing Challenges:

Challenge types - what the numeric challenge type values mean (enum).
Contributing to FreeCodeCamp - Writing ES6 Challenge Tests - a video following Ethan Arrowood as he contributes to the old version of the curriculum.

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