Improve type inference of the returned function #55

src/index.ts

@@ -1,34 +1,37 @@
-/**
- * A function that emits a side effect.
- */
-export type Procedure = (...args: any[]) => any;
-
-export type Options<TT> = {
+export type Options<Result> = {
   isImmediate?: boolean;
   maxWait?: number;
-  callback?: (data: TT) => void;
+  callback?: (data: Result) => void;
 };
 
-export interface DebouncedFunction<F extends Procedure> {
-  (this: ThisParameterType<F>, ...args: Parameters<F>): Promise<ReturnType<F>>;
+export interface DebouncedFunction<
+  Args extends unknown[],
+  F extends (...args: Args) => any
+> {
+  (this: ThisParameterType<F>, ...args: Args): Promise<ReturnType<F>>;
   cancel: (reason?: any) => void;
 }
 
-export function debounce<F extends Procedure>(
+interface DebouncedPromise<FunctionReturn> {
+  resolve: (result: FunctionReturn) => void;
+  reject: (reason?: any) => void;
+}
+
+export function debounce<
+  Args extends unknown[],
+  F extends (...args: Args) => any
+>(
   func: F,
   waitMilliseconds = 50,
   options: Options<ReturnType<F>> = {}
-): DebouncedFunction<F> {
+): DebouncedFunction<Args, F> {
   let timeoutId: ReturnType<typeof setTimeout> | undefined;
   const isImmediate = options.isImmediate ?? false;
   const callback = options.callback ?? false;
   const maxWait = options.maxWait;
   let lastInvokeTime = Date.now();
 
-  let promises: {
-    resolve: (x: ReturnType<F>) => void;
-    reject: (reason?: any) => void;
-  }[] = [];
+  let promises: DebouncedPromise<ReturnType<F>>[] = [];
 
   function nextInvokeTimeout() {
     if (maxWait !== undefined) {
@@ -44,7 +47,7 @@ export function debounce<F extends Procedure>(
 
   const debouncedFunction = function (
     this: ThisParameterType<F>,
-    ...args: Parameters<F>
+    ...args: Args
   ) {
     const context = this;
     return new Promise<ReturnType<F>>((resolve, reject) => {