timers: allow timers to be used as primitives

This allows timers to be matched to numeric Ids and therefore used
as keys of an Object, passed and stored without storing the Timer instance.

clearTimeout/clearInterval is modified to support numeric/string Ids.

Co-authored-by: Bradley Farias <[email protected]>
Co-authored-by: Anatoli Papirovski <[email protected]>

Refs: #21152

doc/api/timers.md

@@ -123,6 +123,21 @@ Calling `timeout.unref()` creates an internal timer that will wake the Node.js
 event loop. Creating too many of these can adversely impact performance
 of the Node.js application.
 
+### `timeout[Symbol.toPrimitive]()`
+<!-- YAML
+added: REPLACEME
+-->
+
+* Returns: {integer} number that can be used to reference this `timeout`
+
+Coerce a `Timeout` to a primitive, a primitive will be generated that
+can be used to clear the `Timeout`.
+The generated number can only be used in the same thread where timeout
+was created. Therefore to use it cross [`worker_threads`][] it has
+to first be passed to a correct thread.
+This allows enhanced compatibility with browser's `setTimeout()`, and
+`setInterval()` implementations.
+
 ## Scheduling timers
 
 A timer in Node.js is an internal construct that calls a given function after
@@ -346,3 +361,4 @@ const timersPromises = require('timers/promises');
 [`setInterval()`]: timers.html#timers_setinterval_callback_delay_args
 [`setTimeout()`]: timers.html#timers_settimeout_callback_delay_args
 [`util.promisify()`]: util.html#util_util_promisify_original
+[`worker_threads`]: worker_threads.html

lib/internal/timers.js

@@ -104,6 +104,8 @@ const {
 const async_id_symbol = Symbol('asyncId');
 const trigger_async_id_symbol = Symbol('triggerId');
 
+const kHasPrimitive = Symbol('kHasPrimitive');
+
 const {
   ERR_INVALID_CALLBACK,
   ERR_OUT_OF_RANGE
@@ -185,6 +187,7 @@ function Timeout(callback, after, args, isRepeat, isRefed) {
   if (isRefed)
     incRefCount();
   this[kRefed] = isRefed;
+  this[kHasPrimitive] = false;
 
   initAsyncResource(this, 'Timeout');
 }
@@ -639,6 +642,7 @@ module.exports = {
   Timeout,
   Immediate,
   kRefed,
+  kHasPrimitive,
   initAsyncResource,
   setUnrefTimeout,
   getTimerDuration,

lib/timers.js

@@ -22,8 +22,10 @@
 'use strict';
 
 const {
+  ObjectCreate,
   MathTrunc,
   Object,
+  SymbolToPrimitive
 } = primordials;
 
 const {
@@ -41,6 +43,7 @@ const {
     kRefCount
   },
   kRefed,
+  kHasPrimitive,
   getTimerDuration,
   timerListMap,
   timerListQueue,
@@ -66,13 +69,21 @@ const {
   emitDestroy
 } = require('internal/async_hooks');
 
+// This stores all the known timer async ids to allow users to clearTimeout and
+// clearInterval using those ids, to match the spec and the rest of the web
+// platform.
+const knownTimersById = ObjectCreate(null);
+
 // Remove a timer. Cancels the timeout and resets the relevant timer properties.
 function unenroll(item) {
   if (item._destroyed)
     return;
 
   item._destroyed = true;
 
+  if (item[kHasPrimitive])
+    delete knownTimersById[item[async_id_symbol]];
+
   // Fewer checks may be possible, but these cover everything.
   if (destroyHooksExist() && item[async_id_symbol] !== undefined)
     emitDestroy(item[async_id_symbol]);
@@ -163,6 +174,14 @@ function clearTimeout(timer) {
   if (timer && timer._onTimeout) {
     timer._onTimeout = null;
     unenroll(timer);
+    return;
+  }
+  if (typeof timer === 'number' || typeof timer === 'string') {
+    const timerInstance = knownTimersById[timer];
+    if (timerInstance !== undefined) {
+      timerInstance._onTimeout = null;
+      unenroll(timerInstance);
+    }
   }
 }
 
@@ -208,6 +227,15 @@ Timeout.prototype.close = function() {
   return this;
 };
 
+Timeout.prototype[SymbolToPrimitive] = function() {
+  const id = this[async_id_symbol];
+  if (!this[kHasPrimitive]) {
+    this[kHasPrimitive] = true;
+    knownTimersById[id] = this;
+  }
+  return id;
+};
+
 function setImmediate(callback, arg1, arg2, arg3) {
   validateCallback(callback);
 

test/parallel/test-timers-to-primitive.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+
+[
+  setTimeout(common.mustNotCall(), 1),
+  setInterval(common.mustNotCall(), 1),
+].forEach((timeout) => {
+  assert.strictEqual(Number.isNaN(+timeout), false);
+  assert.strictEqual(+timeout, timeout[Symbol.toPrimitive]());
+  assert.strictEqual(`${timeout}`, timeout[Symbol.toPrimitive]().toString());
+  assert.deepStrictEqual(Object.keys({ [timeout]: timeout }), [`${timeout}`]);
+  clearTimeout(+timeout);
+});
+
+{
+  // Check that clearTimeout works with number id.
+  const timeout = setTimeout(common.mustNotCall(), 1);
+  const id = +timeout;
+  clearTimeout(id);
+}
+
+{
+  // Check that clearTimeout works with string id.
+  const timeout = setTimeout(common.mustNotCall(), 1);
+  const id = `${timeout}`;
+  clearTimeout(id);
+}