Updated backoff

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@ulms/api-clients",
-  "version": "7.16.0",
+  "version": "7.17.0",
   "description": "JavaScript API clients for ULMS platform",
   "keywords": [],
   "homepage": "https://github.com/foxford/ulms-api-clients-js#readme",

src/backoff.js

@@ -1,18 +1,10 @@
-const FACTOR = 2
+const MIN_DELAY = 500 // 500ms
 const MAX_DELAY = 5 * 60 * 1000 // 5m
-const RANDOM_ADDITIVE_MAX = 1000 // 1s
+const MAX_RANDOM_ADDITIVE = 2000 // 2s
 
 // get milliseconds as value
 const MILLISECONDS_IN_SECOND = 1000
 
-function getRandomIntInclusive(min, max) {
-  const minValue = Math.ceil(min)
-  const maxValue = Math.floor(max)
-
-  // The maximum is inclusive and the minimum is inclusive
-  return Math.floor(Math.random() * (maxValue - minValue + 1) + minValue)
-}
-
 class Backoff {
   constructor() {
     this.counter = 0
@@ -26,18 +18,14 @@ class Backoff {
   }
 
   next() {
-    if (this.delay < MAX_DELAY) {
-      const randomAdditive = getRandomIntInclusive(0, RANDOM_ADDITIVE_MAX)
-
-      // first delay always equals to randomAdditive
-      this.delay =
-        this.counter === 0
-          ? randomAdditive
-          : Math.min(
-              MILLISECONDS_IN_SECOND * FACTOR ** this.counter + randomAdditive,
-              MAX_DELAY,
-            )
-    }
+    this.delay = Math.min(
+      Math.round(
+        MIN_DELAY +
+          MILLISECONDS_IN_SECOND * Math.expm1(this.counter) +
+          MAX_RANDOM_ADDITIVE * Math.random(),
+      ),
+      MAX_DELAY,
+    )
 
     this.counter += 1
   }