diff --git a/lib/util/timers.js b/lib/util/timers.js
index 86fcd9cddeb..08b9ec2aacb 100644
--- a/lib/util/timers.js
+++ b/lib/util/timers.js
@@ -58,17 +58,31 @@ function onTick () {
   // Refresh the fastNow value to the current uptime of the process
   fastNow = performance.now()
 
+  /**
+   * The idx variable is used to iterate over the FastTimeouts array.
+   * Expired FastTimeouts will be removed from the array by being
+   * replaced with the last element in the array. Thus, the idx variable
+   * will only be incremented if the current element is not removed.
+   * @type {number}
+   */
   let idx = 0
+
+  /**
+   * The len variable will contain the length of the FastTimeouts array
+   * and will be decremented when a FastTimeout is removed from the array.
+   * @type {number}
+   */
   let len = FastTimeouts.length
 
   while (idx < len) {
+    /**
+     * @type {FastTimeout}
+     */
     const timer = FastTimeouts[idx]
 
     if (timer.state === PENDING) {
       timer.state = fastNow + timer.delay - TICK_MS
-    }
-
-    if (timer.state > 0 && fastNow >= timer.state) {
+    } else if (timer.state > 0 && fastNow >= timer.state) {
       timer.state = TO_BE_CLEARED
       timer.callback(timer.opaque)
     }
@@ -113,6 +127,18 @@ function refreshTimeout () {
 class FastTimeout {
   [kFastTimeout] = true
 
+  /**
+   * If the state of the timer is a non-negative number, it represents the
+   * time in milliseconds when the timer should expire. Values equal or less
+   * than zero represent the following states:
+   * - NOT_IN_LIST: The timer is not in the list of active timers.
+   * - TO_BE_CLEARED: The timer is in the list of active timers but is marked
+   *  to be cleared.
+   * - PENDING: The timer is in the list of active timers and is waiting for
+   * @type {number}
+   */
+  state = NOT_IN_LIST
+
   /**
    * @constructor
    * @param {Function} callback A function to be executed after the timer expires.
@@ -124,12 +150,6 @@ class FastTimeout {
     this.delay = delay
     this.opaque = opaque
 
-    //  -2 not in timer list
-    //  -1 in timer list but inactive
-    //   0 in timer list waiting for time
-    // > 0 in timer list waiting for time to expire
-    this.state = NOT_IN_LIST
-
     this.refresh()
   }