Add solutions for 3rd module exercises

Author: kasymbayaman

03-callbacks-and-events/3.1-simple-event.js

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+import { EventEmitter } from 'events'
+import { readFile } from 'fs'
+
+class FindRegex extends EventEmitter {
+  constructor (regex) {
+    super()
+    this.regex = regex
+    this.files = []
+  }
+
+  addFile (file) {
+    this.files.push(file)
+    return this
+  }
+
+  find () {
+    // +++ 3.1 added line
+    process.nextTick(() => this.emit('start', this.files));
+    for (const file of this.files) {
+      readFile(file, 'utf8', (err, content) => {
+        if (err) {
+          return this.emit('error', err)
+        }
+
+        this.emit('fileread', file)
+
+        const match = content.match(this.regex)
+        if (match) {
+          match.forEach(elem => this.emit('found', file, elem))
+        }
+      })
+    }
+    return this
+  }
+}
+
+const findRegexInstance = new FindRegex(/hello \w+/)
+findRegexInstance
+  .addFile('fileA.txt')
+  .addFile('fileB.json')
+  .find()
+  .on('found', (file, match) => console.log(`Matched "${match}" in file ${file}`))
+  .on('start', (files) => console.log('Find process started', files)) // +++ added line
+  .on('error', err => console.error(`Error emitted ${err.message}`))

03-callbacks-and-events/3.2-ticker.js

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+import { EventEmitter } from 'events';
+
+// 1 main ticker function
+function ticker(timer, callback) {
+  const eventEmitter = new EventEmitter();
+  let tick = 0;
+  const TICK_INTERVAL = 50;
+
+  const tickStart = new Date();
+
+  const emitTick = () => {
+    emitter.emit('tick', tick);
+    tick++;
+  }
+
+  setTimeout(function recursiveTimeout() {
+    // if timer has passed, terminate and return result
+    if (new Date() - tickStart >= timer) {
+      return callback(null, tick);
+    }
+
+    emitTick();
+
+    // call recursively for next emit
+    setTimeout(recursiveTimeout, TICK_INTERVAL);
+  }, TICK_INTERVAL);
+
+  return eventEmitter;
+}
+
+// 2 initialize ticker event emitter
+const emitter = ticker(1200, (err, tick) => {
+  if (err) {
+    return console.log('Callback error', err);
+  }
+  console.log(`Totally ticked ${tick} times`);
+});
+
+// 3 add listeners
+emitter
+.on('error', err => console.log('Emitted error', err))
+.on('tick', (result) => console.log('Tick #', result));

03-callbacks-and-events/3.3-ticker-mod.js

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+import { EventEmitter } from 'events';
+
+// 1 main ticker function
+function ticker(timer, callback) {
+  const eventEmitter = new EventEmitter();
+  let tick = 0;
+  const TICK_INTERVAL = 50;
+
+  const tickStart = new Date();
+
+  const emitTick = () => {
+    emitter.emit('tick', tick);
+    tick++;
+  }
+
+  // +++ 3.3 added line
+  process.nextTick(emitTick);
+
+  setTimeout(function recursiveTimeout() {
+    // if timer has passed, terminate and return result
+    if (new Date() - tickStart >= timer) {
+      return callback(null, tick);
+    }
+
+    emitTick();
+
+    // call recursively for next emit
+    setTimeout(recursiveTimeout, TICK_INTERVAL);
+  }, TICK_INTERVAL);
+
+  return eventEmitter;
+}
+
+// 2 initialize ticker event emitter
+const emitter = ticker(1200, (err, tick) => {
+  if (err) {
+    return console.log('Callback error', err);
+  }
+  console.log(`Totally ticked ${tick} times`);
+});
+
+// 3 add listeners
+emitter
+.on('error', err => console.log('Emitted error', err))
+.on('tick', (result) => console.log('Tick #', result));

03-callbacks-and-events/3.4-ticker-error-mod.js

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+import { EventEmitter } from 'events';
+
+// 1 main ticker function
+function ticker(timer, callback) {
+  const eventEmitter = new EventEmitter();
+  let tick = 0;
+  const TICK_INTERVAL = 50;
+
+  const tickStart = new Date();
+
+  const emitTick = () => {
+    // +++ 3.4 added code
+    if (Date.now() % 5 === 0) {
+      const err = new Error('Divisible by 5');
+      callback(err);
+      return emitter.emit('error', err);
+    }
+    //
+    emitter.emit('tick', tick);
+    tick++;
+  }
+
+  // +++ 3.3 added line
+  process.nextTick(emitTick);
+
+  setTimeout(function recursiveTimeout() {
+    // if timer has passed, terminate and return result
+    if (new Date() - tickStart >= timer) {
+      return callback(null, tick);
+    }
+
+    emitTick();
+
+    // call recursively for next emit
+    setTimeout(recursiveTimeout, TICK_INTERVAL);
+  }, TICK_INTERVAL);
+
+  return eventEmitter;
+}
+
+// 2 initialize ticker event emitter
+const emitter = ticker(1200, (err, tick) => {
+  if (err) {
+    return console.log('Callback error', err);
+  }
+  console.log(`Totally ticked ${tick} times`);
+});
+
+// 3 add listeners
+emitter
+.on('error', err => console.log('Emitted error', err))
+.on('tick', (result) => console.log('Tick #', result));

package.json

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+{
+  "name": "node.js-design-patterns-solutions",
+  "version": "1.0.0",
+  "main": "index.js",
+  "author": "Baiaman Kasymbaev",
+  "license": "MIT",
+  "type": "module"
+}