timers: introduce setInterval async iterator

Added setInterval async generator to timers\promises. Utilises async generators to provide an iterator compatible with `for await`. Co-Authored-By: Fabian Cook <[email protected]> fix message PR-URL: #37153 Reviewed-By: Benjamin Gruenbaum <[email protected]> Reviewed-By: James M Snell <[email protected]>
nodejs · Feb 3, 2021 · fefc639 · fefc639
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diff --git a/doc/api/timers.md b/doc/api/timers.md
@@ -363,6 +363,38 @@ added: v15.0.0
   * `signal` {AbortSignal} An optional `AbortSignal` that can be used to
     cancel the scheduled `Immediate`.
 
+### `timersPromises.setInterval([delay[, value[, options]]])`
+<!-- YAML
+added: REPLACEME
+-->
+
+Returns an async iterator that generates values in an interval of `delay` ms.
+
+* `delay` {number} The number of milliseconds to wait between iterations.
+   **Default**: `1`.
+* `value` {any} A value with which the iterator returns.
+* `options` {Object}
+  * `ref` {boolean} Set to `false` to indicate that the scheduled `Timeout`
+    between iterations should not require the Node.js event loop to
+    remain active.
+    **Default**: `true`.
+  * `signal` {AbortSignal} An optional `AbortSignal` that can be used to
+    cancel the scheduled `Timeout` between operations.
+
+```js
+(async function() {
+  const { setInterval } = require('timers/promises');
+  const interval = 100;
+  for await (const startTime of setInterval(interval, Date.now())) {
+    const now = Date.now();
+    console.log(now);
+    if ((now - startTime) > 1000)
+      break;
+  }
+  console.log(Date.now());
+})();
+```
+
 [Event Loop]: https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/#setimmediate-vs-settimeout
 [`AbortController`]: globals.md#globals_class_abortcontroller
 [`TypeError`]: errors.md#errors_class_typeerror

diff --git a/lib/timers/promises.js b/lib/timers/promises.js
@@ -18,7 +18,11 @@ const {
   codes: { ERR_INVALID_ARG_TYPE }
 } = require('internal/errors');
 
-const { validateAbortSignal } = require('internal/validators');
+const {
+  validateAbortSignal,
+  validateBoolean,
+  validateObject,
+} = require('internal/validators');
 
 function cancelListenerHandler(clear, reject) {
   if (!this._destroyed) {
@@ -111,7 +115,59 @@ function setImmediate(value, options = {}) {
       () => signal.removeEventListener('abort', oncancel)) : ret;
 }
 
+async function* setInterval(after, value, options = {}) {
+  validateObject(options, 'options');
+  const { signal, ref = true } = options;
+  validateAbortSignal(signal, 'options.signal');
+  validateBoolean(ref, 'options.ref');
+
+  if (signal?.aborted)
+    throw new AbortError();
+
+  let onCancel;
+  let interval;
+  try {
+    let notYielded = 0;
+    let callback;
+    interval = new Timeout(() => {
+      notYielded++;
+      if (callback) {
+        callback();
+        callback = undefined;
+      }
+    }, after, undefined, true, true);
+    if (!ref) interval.unref();
+    insert(interval, interval._idleTimeout);
+    if (signal) {
+      onCancel = () => {
+        // eslint-disable-next-line no-undef
+        clearInterval(interval);
+        if (callback) {
+          callback(PromiseReject(new AbortError()));
+          callback = undefined;
+        }
+      };
+      signal.addEventListener('abort', onCancel, { once: true });
+    }
+
+    while (!signal?.aborted) {
+      if (notYielded === 0) {
+        await new Promise((resolve) => callback = resolve);
+      }
+      for (; notYielded > 0; notYielded--) {
+        yield value;
+      }
+    }
+    throw new AbortError();
+  } finally {
+    // eslint-disable-next-line no-undef
+    clearInterval(interval);
+    signal?.removeEventListener('abort', onCancel);
+  }
+}
+
 module.exports = {
   setTimeout,
   setImmediate,
+  setInterval,
 };