From a9462e6b20cec2199fde2454ed8c2d00771fdc3b Mon Sep 17 00:00:00 2001
From: seognil LC <seognil@gmail.com>
Date: Sat, 22 Aug 2020 18:03:27 +0800
Subject: [PATCH] feat(js): add debounce-promise

---
 js/util/debounce-promise.ts | 58 +++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 js/util/debounce-promise.ts

diff --git a/js/util/debounce-promise.ts b/js/util/debounce-promise.ts
new file mode 100644
index 0000000..a4a6e7d
--- /dev/null
+++ b/js/util/debounce-promise.ts
@@ -0,0 +1,58 @@
+{
+  // * ------------------------------------------------ debounceP
+
+  const debounceP = <T extends any[], K>(fn: (...args: T) => Promise<K>, duration = 0) => {
+    let tick: NodeJS.Timeout;
+
+    let singleP: Promise<K> | null;
+    let singleRes: ((value: K) => void) | null;
+    let singleRej: ((reason?: any) => void) | null;
+
+    return (...args: T) => {
+      if (singleP) {
+        clearTimeout(tick);
+      } else {
+        singleP = new Promise<K>((res, rej) => {
+          singleRes = res;
+          singleRej = rej;
+        });
+      }
+
+      tick = setTimeout(() => {
+        clearTimeout(tick);
+        fn(...args!).then(singleRes, singleRej);
+        singleP = singleRes = singleRej = null;
+      }, duration);
+
+      return singleP;
+    };
+  };
+
+  // * ------------------------------------------------ test
+
+  const delay = (n: number) => new Promise((res) => setTimeout(() => res(), n));
+
+  const fn = async (val: number) => {
+    console.log('run fn, args:', val);
+    await delay(100);
+    return val;
+  };
+
+  const dFn = debounceP(fn, 500);
+
+  // * ----------------
+
+  (async () => {
+    dFn(1).then((e) => (console.log(e), console.assert(e === 3)));
+    dFn(2).then((e) => (console.log(e), console.assert(e === 3)));
+    dFn(3).then((e) => (console.log(e), console.assert(e === 3)));
+
+    console.log('--------');
+    await delay(1000);
+    console.log('--------');
+
+    dFn(6).then((e) => (console.log(e), console.assert(e === 8)));
+    dFn(7).then((e) => (console.log(e), console.assert(e === 8)));
+    dFn(8).then((e) => (console.log(e), console.assert(e === 8)));
+  })();
+}