Promises

Author: prabaprakash

Advance Nodejs/10. Promise Queue Graph.js

@@ -0,0 +1,62 @@
+var logUpdate = require('log-update');
+var toX = () => 'X';
+
+var delay = (seconds) => new Promise((resolves) => {
+    setTimeout(resolves, seconds*1000);
+});
+
+var tasks = [
+  delay(4),
+  delay(6),
+  delay(4),
+  delay(3),
+  delay(5),
+  delay(7),
+  delay(9),
+  delay(10),
+  delay(3),
+  delay(5)
+];
+
+class PromiseQueue {
+
+  constructor(promises=[], concurrentCount=1) {
+    this.concurrent = concurrentCount;
+    this.total = promises.length;
+    this.todo = promises;
+    this.running = [];
+    this.complete = [];
+  }
+
+  get runAnother() {
+    return (this.running.length < this.concurrent) && this.todo.length;
+  }
+
+  graphTasks() {
+    var { todo, running, complete } = this;
+    logUpdate(`
+
+   todo: [${todo.map(toX)}]
+   running: [${running.map(toX)}]
+   complete: [${complete.map(toX)}]
+
+    `);
+  }
+
+  run() {
+    while (this.runAnother) {
+      var promise = this.todo.shift();
+      promise.then(() => {
+        this.complete.push(this.running.shift());
+        this.graphTasks();
+        this.run();
+      })
+      this.running.push(promise);
+      this.graphTasks();
+    }
+  }
+
+}
+
+var delayQueue = new PromiseQueue(tasks, 2);
+delayQueue.run();

Advance Nodejs/7.1. Async.js

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+var fs = require('fs');
+var { promisify } = require('util');
+var writeFile = promisify(fs.writeFile);
+var unlink = promisify(fs.unlink);
+var readdir = promisify(fs.readdir);
+var beep = () => process.stdout.write("\x07");
+var delay = (seconds) => new Promise((resolves) => {
+    setTimeout(resolves, seconds*1000);
+})
+
+async function start() {
+
+  var files = await readdir(__dirname);
+  console.log(files);
+
+}
+
+start();

Advance Nodejs/8. Promise.all.js

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+var fs = require('fs');
+var { promisify } = require('util');
+var writeFile = promisify(fs.writeFile);
+var unlink = promisify(fs.unlink);
+var readdir = promisify(fs.readdir);
+var beep = () => process.stdout.write("\x07");
+var delay = (seconds) => new Promise((resolves) => {
+    setTimeout(resolves, seconds*1000);
+})
+
+Promise.all([
+  delay(5),
+  delay(2),
+  delay(3),
+  delay(5)
+]).then(() => readdir(__dirname))
+  .then(console.log);
+
+
+Promise.race([
+    delay(5),
+    delay(2),
+    delay(3),
+    delay(5)
+  ]).then(() => readdir(__dirname))
+    .then(console.log);

Advance Nodejs/9. PromiseQueue.js

@@ -0,0 +1,62 @@
+var logUpdate = require('log-update');
+var toX = () => 'X';
+
+var delay = (seconds) => new Promise((resolves) => {
+    setTimeout(resolves, seconds*1000);
+});
+
+var tasks = [
+  delay(4),
+  delay(6),
+  delay(4),
+  delay(3),
+  delay(5),
+  delay(7),
+  delay(9),
+  delay(10),
+  delay(3),
+  delay(5)
+];
+
+class PromiseQueue {
+
+  constructor(promises=[], concurrentCount=1) {
+    this.concurrent = concurrentCount;
+    this.total = promises.length;
+    this.todo = promises;
+    this.running = [];
+    this.complete = [];
+  }
+
+  get runAnother() {
+    return (this.running.length < this.concurrent) && this.todo.length;
+  }
+
+  graphTasks() {
+    var { todo, running, complete } = this;
+    logUpdate(`
+
+   todo: [${todo.map(toX)}]
+   running: [${running.map(toX)}]
+   complete: [${complete.map(toX)}]
+
+    `);
+  }
+
+  run() {
+    while (this.runAnother) {
+      var promise = this.todo.shift();
+      promise.then(() => {
+        this.complete.push(this.running.shift());
+        this.graphTasks();
+        this.run();
+      })
+      this.running.push(promise);
+      this.graphTasks();
+    }
+  }
+
+}
+
+var delayQueue = new PromiseQueue(tasks, 2);
+delayQueue.run();