1 files changed, 52 insertions, 0 deletions
diff --git a/packages/webapi/src/lib/ContextEvent.ts b/packages/webapi/src/lib/ContextEvent.ts
new file mode 100644
index 000000000..98cd72de5
--- /dev/null
+++ b/packages/webapi/src/lib/ContextEvent.ts
@@ -0,0 +1,52 @@
+import { Event } from 'event-target-shim'
+
+/** An event fired by a context requester to signal it desires a named context. */
+export class ContextEvent<T = unknown> extends Event<'context-request'> {
+	constructor(init: ContextEventInit<T>) {
+		super('context-request', { bubbles: true, composed: true })
+
+		init = Object(init) as Required<ContextEventInit<T>>
+
+		this.context = init.context
+	}
+
+	context!: Context<T>
+	multiple!: boolean
+	callback!: ContextCallback<Context<T>>
+}
+
+interface ContextEventInit<T = unknown> {
+	context: Context<T>
+	multiple?: boolean
+	callback: ContextCallback<Context<T>>
+}
+
+/** A Context object defines an optional initial value for a Context, as well as a name identifier for debugging purposes. */
+export type Context<T = unknown> = {
+	name: string
+	initialValue?: T
+}
+
+/** A helper type which can extract a Context value type from a Context type. */
+export type ContextType<T extends Context> = T extends Context<infer Y> ? Y : never
+
+/** A function which creates a Context value object */
+export function createContext<T>(name: string, initialValue?: T): Readonly<Context<T>> {
+	return {
+		name,
+		initialValue,
+	}
+}
+
+/** A callback which is provided by a context requester and is called with the value satisfying the request. */
+export type ContextCallback<ValueType> = (
+	value: ValueType,
+	dispose?: () => void
+) => void
+
+declare global {
+	interface HTMLElementEventMap {
+		/** A 'context-request' event can be emitted by any element which desires a context value to be injected by an external provider. */
+		'context-request': ContextEvent
+	}
+}