@jupyterlab/ui-components/README.md

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# @jupyterlab/ui-components

The
[@jupyterlab/ui-components](https://jupyterlab.github.io/jupyterlab/modules/_ui_components_src_index_.html)
package provides UI elements that are widely used in JupyterLab core,
and that can be reused in your own extensions.

For example, all of the icons in JupyterLab core can be reused via
`LabIcon`. You can also use `LabIcon` to create your own custom icons
that will be able to automatically change color to match the current
JupyterLab theme.

# `LabIcon` - set up and render icons

`LabIcon` is the icon class used by JupyterLab, and is part of the new
icon system introduced in JupyterLab v2.0.

## How JupyterLab handles icons

The @jupyterlab/ui-components package provides icons to the rest of
JupyterLab, in the form of a set of `LabIcon` instances (currently about
80). All of the icons in the core JupyterLab packages are rendered using
one of these `LabIcon` instances.

## Using the icons in your own code

You can use any of JupyterLab icons in your own code via an `import`
statement. For example, to use `jupyterIcon` you would first do:

```typescript
import { jupyterIcon } from '@jupyterlab/ui-components';
```

## How to render an icon into a DOM node

Icons can be added as children to any `div` or `span` nodes using the
`icon.element(...)` method (where `icon` is any instance of `LabIcon`).
For example, to render the Jupyter icon you could do:

```typescript
jupyterIcon.element({
  container: elem,
  height: '16px',
  width: '16px',
  marginLeft: '2px'
});
```

where `elem` is any `HTMLElement` with a `div` or `span` tag. As shown
in the above example, the icon can be styled by passing CSS parameters
into `.element(...)`. Any valid CSS parameter can be used (one catch:
snake case params do have to be converted to camel case: instead of
`foo-bar: '8px'`, you’d need to use `fooBar: '8px'`.

## How to render an icon as a React component

Icons can also be rendered using React. The `icon.react` parameter holds
a standard React component that will display the icon on render. Like
any React component, `icon.react` can be used in various ways.

For example, here is how you would add the Jupyter icon to the render
tree of another React component:

```jsx
public render() {
  return (
    <div className="outer">
      <div className="inner">
        <jupyterIcon.react tag="span" right="7px" top="5px" />
        "and here's a text node"
      </div>
    </div>
  );
}
```

Alternatively, you can just render the icon directly into any existing
DOM node `elem` by using the `ReactDOM` module:

```typescript
ReactDOM.render(jupyterIcon.react, elem);
```

If do you use `ReactDOM` to render, and if the `elem` node is ever
removed from the DOM, you’ll first need to clean it up:

```typescript
ReactDOM.unmountComponentAtNode(elem);
```

This cleanup step is not a special property of `LabIcon`, but is instead
needed for any React component that is rendered directly at the top
level by `ReactDOM`: failure to call `unmountComponentAtNode` can result
in a [memory leak](https://stackoverflow.com/a/48198011/425458).

## How to create your own custom `LabIcon`

You can create your own custom icon by constructing a new instance of
`LabIcon`:

```typescript
export const fooIcon = new LabIcon({
  name: 'barpkg:foo',
  svgstr: '<svg>...</svg>'
});
```

where `name` should be of the form “your-pkg:icon-name”, and `svgstr` is
the raw contents of your icon’s svg file.

## How to create a new `LabIcon` from an external svg file

Although you can copy-and-paste an svg directly into the `LabIcon`
constructor, the best practice is to keep the svg for each of your icons
in its own separate svg file. You will need to have an `svg.d.ts` file
at the root of your project’s `src` directory:

```typescript
// svg.d.ts

declare module '*.svg' {
  const value: string;
  export default value;
}
```

You can then `import` the contents of an svg file:

```typescript
import fooSvgstr from 'path-to-your/foo.svg';

export const fooIcon = new LabIcon({
  name: 'barpkg:foo',
  svgstr: fooSvgstr
});
```

## Sync icon color to JupyterLab theme

<em>Example svgs with class annotation can be found in <a href="https://github.com/jupyterlab/jupyterlab/tree/f0153e0258b32674c9aec106383ddf7b618cebab/packages/ui-components/style/icons">ui-components/style/icons</a></em>

You can ensure that the colors of your custom `LabIcon` sync up to the
colors of the current JupyterLab theme by adding appropriate `class`
annotations to each colored element of your icon's svg.

In other words, each element of your svg that a `fill="..."` or a
`stroke="..."` property should also have a `class="jp-icon<whatever>"`
property.

### Available icon classes

<em>Icon-related CSS classes are defined in <a href="https://github.com/jupyterlab/jupyterlab/blob/f0153e0258b32674c9aec106383ddf7b618cebab/packages/ui-components/style/icons.css">ui-components/style/icons.css</a></em>

All colors shown are for the standard light/dark theme, mouse over for
hex values.

#### `jp-iconX`: contrast to theme background

<ul>
<li>jp-icon0: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#111"/><title>#111</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#fff"/><title>#fff</title></svg></li>
<li>jp-icon1: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#212121"/><title>#212121</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#fff"/><title>#fff</title></svg></li>
<li>jp-icon2: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#424242"/><title>#424242</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#eee"/><title>#eee</title></svg></li>
<li>jp-icon3: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#616161"/><title>#616161</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#bdbdbd"/><title>#bdbdbd</title></svg></li>
<li>jp-icon4: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#757575"/><title>#757575</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#757575"/><title>#757575</title></svg></li>
</ul>

Most one-color icons in JupyterLab (including the sidebar and toolbar
icons) are colored using the `jp-icon3` class.

For light/dark themes, `jp-icon0` corresponds to the darkest/lightest
background color, while `jp-icon1` is somewhat lighter/darker, and so
forth.

#### `jp-icon-accentX`: match to theme background

<ul>
<li>jp-icon-accent0: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#fff"/><title>#fff</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#111"/><title>#111</title></svg></li>
<li>jp-icon-accent1: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#fff"/><title>#fff</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#212121"/><title>#212121</title></svg></li>
<li>jp-icon-accent2: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#eee"/><title>#eee</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#424242"/><title>#424242</title></svg></li>
<li>jp-icon-accent3: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#bdbdbd"/><title>#bdbdbd</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#616161"/><title>#616161</title></svg></li>
<li>jp-icon-accent4: <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#757575"/><title>#757575</title></svg> / <svg width="16" viewBox="0 0 1 1"><rect width="1" height="1" fill="#757575"/><title>#757575</title></svg></li>
</ul>

For light/dark themes, `jp-icon-accent0` corresponds to the
lightest/darkest background color, while `jp-icon-accent1` is somewhat
darker/lighter, and so forth.

### Adding classes to a one-color icon

For most simple, one-color icons, it is desirable for the icon's color
to strongly contrast with that of the application's background. You can
achieve this using one of the `jp-iconX` classes.

**Example: check icon**

_svg source:_

```html
<svg xmlns="http://www.w3.org/2000/svg" width="100" viewBox="0 0 24 24">
  <path
    class="jp-icon3"
    fill="#616161"
    d="M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z"
  />
</svg>
```

_rendered icon:_

<svg xmlns="http://www.w3.org/2000/svg" width="100" viewBox="0 0 24 24">
  <path class="jp-icon3" fill="#616161" d="M9 16.17L4.83 12l-1.42 1.41L9 19 21 7l-1.41-1.41z"/>
</svg>

### Adding classes to a multi-colored icon

For more complex icons, each element that needs to match the background
should be annotated with a `jp-icon-accentX` class, while each element
that needs to contrast with the background should be annotated with a
`jp-iconX` class.

**Example: close-circle icon**

_svg source:_

```html
<svg xmlns="http://www.w3.org/2000/svg" width="100" viewBox="0 0 24 24">
  <circle class="jp-icon3" fill="#616161" cx="12" cy="12" r="11" />
  <rect
    class="jp-icon-accent0"
    fill="#fff"
    height="18"
    width="2"
    x="11"
    y="3"
    transform="rotate(315, 12, 12)"
  />
  <rect
    class="jp-icon-accent0"
    fill="#fff"
    height="18"
    width="2"
    x="11"
    y="3"
    transform="rotate(45, 12, 12)"
  />
</svg>
```

_rendered icon:_

<svg xmlns="http://www.w3.org/2000/svg" width="100" viewBox="0 0 24 24">
  <circle class="jp-icon3" fill="#616161" cx="12" cy="12" r="11"/>
  <rect class="jp-icon-accent0" fill="#fff" height="18" width="2" x="11" y="3" transform="rotate(315, 12, 12)"/>
  <rect class="jp-icon-accent0" fill="#fff" height="18" width="2" x="11" y="3" transform="rotate(45, 12, 12)"/>
</svg>

## Background

### Icon handling in Jupyterlab

Pre JupyterLab 2.0, most icons were created using the
icons-as-css-background pattern:

- Set up the icon’s svg as a `background-image` in CSS:

  ```css
  /* CSS */

  .jp-FooIcon {
    background-image: url('path-to-your/foo.svg');
  }
  ```

- Add the icon to the DOM by constructing an otherwise empty DOM node
  with the appropriate class:

  ```typescript
  // typescript

  const e = document.createElement('div');
  e.className = 'jp-FooIcon';
  document.body.append(e);
  ```

What you end up with is a single DOM node that has the “foo” icon as a
background image.

Post JupyterLab 2.0, nearly all icons in core are now created using
[LabIcon](https://github.com/jupyterlab/jupyterlab/blob/f0153e0258b32674c9aec106383ddf7b618cebab/packages/ui-components/src/icon/labicon.tsx)
and the icons-as-inline-svg pattern:

- Construct a new instance of LabIcon from the icon’s name and svg:

  ```typescript
  // typescript

  // svgstr is the raw contents of an icon's svg file
  export const fooIcon = new LabIcon({
    name: 'barpkg:foo',
    svgstr: '<svg>...</svg>'
  });
  ```

- Add the icon to the DOM using the appropriate property of your
  LabIcon instance (either LabIcon.element() to directly create a DOM
  node, or LabIcon.react to get the icon as a react component):

  ```typescript
  // typescript

  const e = fooIcon.element();
  document.body.append(e);
  ```

What you end up with is a DOM node (by default a ‘div’) that has an
inline svg node as a child.

### `background-image` vs inline svg

The big limitation of the old icon-as-css-background pattern is that svg
images rendered as `background-image` are invisible to CSS. On the other
hand, an icon rendered as an inline svg node is fully exposed to the
CSS. This allows us to dynamically change icon styling as needed simply by
modifying our CSS. Most importantly, this allows us to recolor icons
according to Jupyterlab’s current theme.