Add definitions for WeakRef and FinalizationRegistry

src/lib/esnext.d.ts

@@ -2,3 +2,4 @@
 /// <reference lib="esnext.intl" />
 /// <reference lib="esnext.string" />
 /// <reference lib="esnext.promise" />
+/// <reference lib="esnext.weakref" />

src/lib/esnext.weakref.d.ts

@@ -0,0 +1,55 @@
+interface WeakRef<T extends object> {
+    readonly [Symbol.toStringTag]: "WeakRef";
+
+    /**
+     * Returns the WeakRef instance's target object, or undefined if the target object has been
+     * reclaimed.
+     */
+    deref(): T | undefined;
+}
+
+interface WeakRefConstructor {
+    readonly prototype: WeakRef<any>;
+
+    /**
+     * Creates a WeakRef instance for the given target object.
+     * @param target The target object for the WeakRef instance.
+     */
+    new<T extends object>(target?: T): WeakRef<T>;
+}
+
+declare var WeakRef: WeakRefConstructor;
+
+interface FinalizationRegistry {
+    readonly [Symbol.toStringTag]: "FinalizationRegistry";
+
+    /**
+     * Registers an object with the registry.
+     * @param target The target object to register.
+     * @param heldValue The value to pass to the finalizer for this object. This cannot be the
+     * target object.
+     * @param unregisterToken The token to pass to the unregister method to unregister the target
+     * object. If provided (and not undefined), this must be an object. If not provided, the target
+     * cannot be unregistered.
+     */
+    register(target: object, heldValue: any, unregisterToken?: object): void;
+
+    /**
+     * Unregisters an object from the registry.
+     * @param unregisterToken The token that was used as the unregisterToken argument when calling
+     * register to register the target object.
+     */
+    unregister(unregisterToken: object): void;
+}
+
+interface FinalizationRegistryConstructor {
+    readonly prototype: FinalizationRegistry;
+
+    /**
+     * Creates a finalization registry with an associated cleanup callback
+     * @param cleanupCallback The callback to call after an object in the registry has been reclaimed.
+     */
+    new(cleanupCallback: (heldValue: any) => void): FinalizationRegistry;
+}
+
+declare var FinalizationRegistry: FinalizationRegistryConstructor;