add: Throttle Queue

Author: supercodestart

README.md

@@ -6,4 +6,5 @@
 - [Fixing setting up a callback](fixing-setting-up-a-callback)
 - [Getting the distinct transactions](getting-the-distinct-transactions)
 - [Replacing with the cipher letters](replacing-with-the-cipher-letters)
+- [Throttle Queue](throttle-queue)
 - [Validating a maze path](validating-a-maze-path)

throttle-queue/README.md

@@ -0,0 +1,13 @@
+# Throttle Queue
+
+Build an app that runs no more than `n` queue functions at once.
+
+- Run up to N functions in the Queue
+- When one (each) completes, run another if there are any
+- When ALL functions in queue are resolved, return the results array
+
+## Execute
+
+```bash
+node solution.js
+```

throttle-queue/solution.js

@@ -0,0 +1,60 @@
+function getRandomInt(max) {
+  return Math.floor(Math.random() * max);
+}
+
+let i = 0;
+
+function returnSlow() {
+  return new Promise((resolve) => {
+    const myI = i;
+    i++;
+    console.log('started ' + myI);
+    setTimeout(() => {
+      console.log('ended ' + myI);
+      resolve(getRandomInt(10));
+    }, getRandomInt(8) * 100 + 200);
+  });
+}
+
+function throttle1(queue, acc) {
+  if (queue.length) {
+    const fn = queue.shift();
+    return fn().then((result) => {
+      // I have result and rest of queue
+      const resultAcc = acc || [];
+      resultAcc.push(result);
+
+      if (!queue.length) return resultAcc;
+      return throttle1(queue, resultAcc);
+    });
+  }
+}
+
+function throttleQ(queue, n, result) {
+  let subQueue = [];
+
+  while (queue.length && subQueue.length < n) {
+    subQueue.push(queue.shift());
+  }
+
+  return Promise.all(subQueue.map((fn) => fn())).then(
+    (subResult) => {
+      const resultAcc = [...(result ?? []), ...subResult];
+      return queue.length
+        ? throttleQ(queue, n, resultAcc)
+        : resultAcc;
+    },
+  );
+}
+
+(async () => {
+  const fns = [...Array(25)].map((_, i) =>
+    returnSlow.bind(null, i),
+  );
+
+  const promises = await throttleQ(fns, 6);
+
+  const data = await Promise.all(promises);
+
+  console.log({ data });
+})();