From e9769b07218601352f3164d7dfb0f8b8252aa6ec Mon Sep 17 00:00:00 2001
From: Andrew Kingston <andrew@kingston.dev>
Date: Sat, 8 Oct 2022 15:03:44 +0100
Subject: [PATCH] Add throttle utility as an improved debounce

---
 packages/frontend-core/src/utils/utils.js | 36 +++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/packages/frontend-core/src/utils/utils.js b/packages/frontend-core/src/utils/utils.js
index 587d057351..ed76f13494 100644
--- a/packages/frontend-core/src/utils/utils.js
+++ b/packages/frontend-core/src/utils/utils.js
@@ -4,6 +4,8 @@
  * @param fn the async function to run
  * @return {Promise} a sequential version of the function
  */
+import { lastIndexOf } from "lodash/array"
+
 export const sequential = fn => {
   let queue = []
   return async (...params) => {
@@ -40,3 +42,37 @@ export const debounce = (callback, minDelay = 1000) => {
     })
   }
 }
+
+/**
+ * Utility to throttle invocations of a synchronous function. This is better
+ * than a simple debounce invocation for a number of reasons. Features include:
+ * - First invocation is immediate (no initial delay)
+ * - Every invocation has the latest params (no stale params)
+ * - There will always be a final invocation with the last params (no missing
+ *   final update)
+ * @param callback
+ * @param minDelay
+ * @returns {Function} a throttled version function
+ */
+export const throttle = (callback, minDelay = 1000) => {
+  let lastParams
+  let stalled = false
+  let pending = false
+  const invoke = (...params) => {
+    lastParams = params
+    if (stalled) {
+      pending = true
+      return
+    }
+    callback(...lastParams)
+    stalled = true
+    setTimeout(() => {
+      stalled = false
+      if (pending) {
+        pending = false
+        invoke(...lastParams)
+      }
+    }, minDelay)
+  }
+  return invoke
+}