feat: support attribute format for some properties

This allows users to set the locale, data source, and skin tone
emoji using HTML attributes as well as properties.

Fixes #7

README.md

@@ -233,10 +233,10 @@ The `new Picker(options)` constructor supports several options:
 Name | Type | Default | Description |
 ------ | ------ | ------ | ------ |
 `customEmoji` | CustomEmoji[] | - | Array of custom emoji  |
-`dataSource` | string | "https://cdn.jsdelivr.net/npm/emojibase-data@5/en/data.json" | URL to fetch the emojibase data from |
+`dataSource` | string | "https://cdn.jsdelivr.net/npm/emojibase-data@5/en/data.json" | URL to fetch the emojibase data from (`data-source` when used as an attribute) |
 `i18n` | I18n | - | i18n object (see below for details) |
 `locale` | string | "en" | Locale string |
-`skinToneEmoji` | string | "🖐️" | The emoji to use for the skin tone picker |
+`skinToneEmoji` | string | "🖐️" | The emoji to use for the skin tone picker (`skin-tone-emoji` when used as an attribute) |
 
 
 
@@ -251,13 +251,26 @@ const picker = new Picker({
 })
 ```
 
-These values can also be set at runtime, e.g.:
+These values can also be set at runtime:
 
 ```js
 const picker = new Picker();
 picker.dataSource = '/my-emoji.json';
 ```
 
+Some values can also be set as declarative attributes:
+
+```html
+<emoji-picker
+  locale="fr"
+  data-source="/fr-emoji.json"
+  skin-tone-emoji="✌"
+></emoji-picker>
+```
+
+Note that complex properties like `i18n` or `customEmoji` are not supported as attributes, because the DOM only
+supports string attributes, not complex objects.
+
 #### i18n structure
 
 Here is the default English `i18n` object (`"en"` locale):

src/picker/PickerElement.js

@@ -15,6 +15,19 @@ export default class Picker extends SveltePicker {
     log('disconnectedCallback')
     this.$destroy()
   }
+
+  static get observedAttributes () {
+    return ['locale', 'data-source', 'skin-tone-emoji'] // complex objects aren't supported, also use kebab-case
+  }
+
+  // via https://github.com/sveltejs/svelte/issues/3852#issuecomment-665037015
+  attributeChangedCallback (attrName, oldValue, newValue) {
+    super.attributeChangedCallback(
+      attrName.replace(/-([a-z])/g, (_, up) => up.toUpperCase()),
+      oldValue,
+      newValue
+    )
+  }
 }
 
 customElements.define('emoji-picker', Picker)

src/types/picker.ts

@@ -9,10 +9,10 @@ export default class Picker extends HTMLElement {
 
   /**
    *
-   * @param dataSource - URL to fetch the emojibase data from
+   * @param dataSource - URL to fetch the emojibase data from (`data-source` when used as an attribute)
    * @param locale - Locale string
    * @param i18n - i18n object (see below for details)
-   * @param skinToneEmoji - The emoji to use for the skin tone picker
+   * @param skinToneEmoji - The emoji to use for the skin tone picker (`skin-tone-emoji` when used as an attribute)
    * @param customEmoji - Array of custom emoji
    */
   constructor({

test/spec/picker/attributes.test.js

@@ -0,0 +1,47 @@
+import { basicAfterEach, basicBeforeEach, FR_EMOJI, ALL_EMOJI, mockFrenchDataSource, tick } from '../shared'
+import Picker from '../../../src/picker/PickerElement.js'
+import { getByRole } from '@testing-library/dom'
+
+describe('attributes tests', () => {
+  beforeEach(async () => {
+    basicBeforeEach()
+    mockFrenchDataSource()
+  })
+
+  afterEach(basicAfterEach)
+
+  test('setting initial locale/dataSource issues only one GET', async () => {
+    const picker = new Picker()
+    picker.setAttribute('locale', 'fr')
+    picker.setAttribute('data-source', FR_EMOJI)
+    document.body.appendChild(picker)
+    await tick(20)
+
+    expect(fetch).toHaveBeenCalledTimes(1)
+    expect(fetch).toHaveBeenLastCalledWith(FR_EMOJI, undefined)
+
+    expect(picker.locale).toEqual('fr')
+    expect(picker.dataSource).toEqual(FR_EMOJI)
+    expect(picker.getAttribute('locale')).toEqual('fr')
+    expect(picker.getAttribute('data-source')).toEqual(FR_EMOJI)
+  })
+
+  test('can set skintone emoji using an attribute', async () => {
+    const picker = new Picker()
+    picker.setAttribute('data-source', ALL_EMOJI)
+    picker.setAttribute('skin-tone-emoji', '✌')
+    document.body.appendChild(picker)
+    await tick(20)
+    expect(getByRole(picker.shadowRoot, 'button', { name: /Choose a skin tone/ }).innerHTML)
+      .toContain('✌')
+    expect(picker.skinToneEmoji).toEqual('✌')
+    expect(picker.getAttribute('skin-tone-emoji')).toEqual('✌')
+    expect(picker.locale).toEqual('en')
+
+    picker.setAttribute('skin-tone-emoji', '🏃')
+    await tick(20)
+    expect(getByRole(picker.shadowRoot, 'button', { name: /Choose a skin tone/ }).innerHTML)
+      .toContain('🏃')
+    expect(picker.skinToneEmoji).toEqual('🏃')
+  })
+})