# code-playground

Code Playground is a web component to display an editable and executable code
section in a web page.

To use it, add a script tag pointing to the code for the component:

```html
<script type="module" src="../dist/code-playground.min.js"></script>
```

Then add a `<code-playground>` tag in your page:

```html
<code-playground>
  <div slot="javascript">console.log("Hello world")</div>
</code-playground>
```

Add one or more `<div>` with a `slot` attribute indicating the type of content:
"javascript", "html" or "css".

If there are multiple "slots", each will be displayed in a separate tab or
section.

If CodeMirror is included in the page, it will be used as the editor for the
content. To include it, add these script tags to your page:

```html
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.11/codemirror.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.11/mode/javascript/javascript.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.11/mode/xml/xml.min.js"></script>
```

If the attribute `autorun=never` is present, pres **Run** to execute the code
after changing it.

To revert your changes and restore the initial content, press **Reset**.

The JavaScript source code is modified before execution to be executable in a
'sandbox':

- the `console` calls, such as `console.log()` are intercepted so they are
  displayed in the playground rather than in the browser's console
- the `document.querySelector()`,
  'document.querySelectorAll()` and 'document.getElementById()` calls are also
  intercepted to respect the scope of the playground, that is using these calls
  you can also access content in the playground. This means you can also have
  multiple elements with the same ID in different playgrounds, and the correct
  one will be selected.
- if a `style` slot is provided, its content is injected as a CSS stylesheet
  before the script execution

```html
<code-playground layout="stack" show-line-numbers>
  <style slot="style">
    .grey-zone {
      background: grey;
      height: 100px;
      width: 100%;
    }
  </style>
  <div slot="html">&lt;div class="grey-zone"&gt;&lt\div&gt;</div>
</code-playground>
```

- if a `preamble` slot is provided, it is inserted before the script.
- if a `output-stylesheets` attribute is provided, it is used to insert links to
  stylesheets in the output.
- the path of `import` directives can be modified as well. Add a `<script>` tag
  inside the component that defines a `moduleMap` variable that maps a module
  name to a URL. For example:

```html
<code-playground>
  <script>
    moduleMap = {
      mathlive: "//unpkg.com/mathlive/dist/mathlive.min.mjs",
    };
  </script></code-playground>
  <div slot="javascript">import MathLive from 'mathlive';</div>
</code-playground>
```

will result in the `"mathlive"` module to be loaded from the
`"//unpkg.com/mathlive/dist/mathlive.min.mjs"` URL;

# Attributes and Properties

The attributes can be specified directly on the component, e.g.

```html
<code-playground layout="stack">
  <div slot="javascript">...</div>
  <div slot="html">...</div>
</code-playground>
```

There are corresponding properties for the attributes which can be accessed via
JavaScript.

| Attribute               | Property              |                                                                                                                                                                      |
| ----------------------- | --------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `layout`                |                       | `stack` (each section is displayed in a column) or `tabs` (each section is displayed in a panel with a tab selector)                                                 |
| `active-tab`            | `activeTab`           | `html`, `javascript` or `css`: indicate which tab is visible if the layout is `tab`                                                                                  |
| `show-line-numbers`     | `showLineNumbers`     | `true` or `false`. If true, displays line numbers in the gutter of the source code.                                                                                  |
| `button-bar-visibility` | `buttonBarVisibility` | `visible`: always show the button bar, `hidden`: never show the button bar, `auto`: show the button bar when the content is modified                                 |
| `autorun`               | `autorun`             | `never`: the **Run** button must be pressed to see changes, otherwise a number indicating a lag in millisecond between editing changes and re-running the playground |