[examples] Add bespoke JS version of Context Basics (#1233)

Author: augustjk

packages/lit-dev-content/samples/examples/context-basics/elements.js

@@ -0,0 +1,63 @@
+import {html, LitElement} from 'lit';
+import {ContextProvider, ContextConsumer, createContext} from '@lit/context';
+
+import {providerStyles} from './styles.js';
+
+const contextKey = Symbol('contextKey');
+
+// Context object, which acts like a key for the context.
+// The context object acts as a key. A consumer will only receive
+// values from a provider if their contexts match. A Symbol ensures
+// that this context will be unique.
+const context = createContext(contextKey);
+
+export class ProviderEl extends LitElement {
+  static styles = providerStyles;
+
+  static properties = {
+    data: {},
+  };
+
+  constructor() {
+    super();
+    this._provider = new ContextProvider(this, {context});
+    this.data = 'Initial';
+  }
+
+  /**
+   * `data` will be provided to any consumer that is in the DOM tree below it.
+   */
+  set data(value) {
+    this._data = value;
+    this._provider.setValue(value);
+  }
+
+  get data() {
+    return this._data;
+  }
+
+  render() {
+    return html`
+      <h3>Provider's data: <code>${this.data}</code></h3>
+      <slot></slot>
+    `;
+  }
+}
+customElements.define('provider-el', ProviderEl);
+
+export class ConsumerEl extends LitElement {
+  _consumer = new ContextConsumer(this, {context});
+
+  /**
+   * `providedData` will be populated by the first ancestor element which
+   * provides a value for `context`.
+   */
+  get providedData() {
+    return this._consumer.value;
+  }
+
+  render() {
+    return html`<h3>Consumer data: <code>${this.providedData}</code></h3>`;
+  }
+}
+customElements.define('consumer-el', ConsumerEl);

packages/lit-dev-content/samples/examples/context-basics/elements.ts

@@ -12,7 +12,7 @@ type ContextValue = string;
 // The context object acts as a key. A consumer will only receive
 // values from a provider if their contexts match. A Symbol ensures
 // that this context will be unique.
-const context = createContext<ContextValue>(Symbol());
+const context = createContext<ContextValue>(contextKey);
 
 @customElement('provider-el')
 export class ProviderEl extends LitElement {
@@ -43,7 +43,7 @@ export class ConsumerEl extends LitElement {
   providedData = '';
 
   render() {
-    return html` <h3>Consumer data: <code>${this.providedData}</code></h3> `;
+    return html`<h3>Consumer data: <code>${this.providedData}</code></h3>`;
   }
 }