Add TypeScript definitions

lib/index.d.ts

@@ -0,0 +1,46 @@
+export default class SelectorObserver {
+  constructor(rootNode: Node)
+  disconnect(): void
+  observe: typeof observe
+}
+
+export declare function observe<T extends Element>(
+  selector: string,
+  options: {
+    constructor: {new (): T}
+  } & Options<T>
+): Observer
+export declare function observe<T extends Element>(
+  options: {
+    selector: string
+    constructor: {new (): T}
+  } & Options<T>
+): Observer
+export declare function observe(selector: string, initialize: InitializerCallback<Element>): Observer
+export declare function observe(selector: string, options: Options<Element>): Observer
+export declare function observe(options: {selector: string} & Options<Element>): Observer
+
+type Options<T> = {
+  initialize?: InitializerCallback<T>
+  add?: AddCallback<T>
+  remove?: RemoveCallback<T>
+  subscribe?: SubscribeCallback<T>
+}
+
+type InitializerCallback<T> = (el: T) => void | InitializerCallbacks<T>
+type AddCallback<T> = (el: T) => void
+type RemoveCallback<T> = (el: T) => void
+type SubscribeCallback<T> = (el: T) => Subscription
+
+type InitializerCallbacks<T> = {
+  add?: AddCallback<T>
+  remove?: RemoveCallback<T>
+}
+
+type Observer = {
+  abort(): void
+}
+
+interface Subscription {
+  unsubscribe(): void
+}