feat(streams): started the streams example implementation

Author: bahmutov

src/12-streams.js

@@ -0,0 +1,52 @@
+'use strict';
+
+var numbers = [3, 1, 7];
+var constant = 2;
+
+function mul(a, b) {
+  return a * b;
+}
+function print(n) {
+  console.log(n);
+}
+var byConstant = mul.bind(null, constant);
+
+// stream of numbers from an Array
+var util = require('util');
+var Readable = require('stream').Readable;
+util.inherits(NumberStream, Readable);
+
+function NumberStream(numbers) {
+  Readable.call(this, {
+    objectMode: true
+  });
+  this.numbers = numbers;
+  this.index = 0;
+}
+
+NumberStream.prototype._read = function _read() {
+  // utility functions for clarity
+  function outputNextNumber() {
+    this.push(this.numbers[this.index++]);
+  }
+
+  function isFinished() {
+    return this.index >= this.numbers.length;
+  }
+
+  outputNextNumber.call(this);
+  if (isFinished.call(this)) {
+    this.push(null);
+  }
+};
+
+var numbers_ = new NumberStream(numbers);
+
+// to just print the numbers
+/*
+numbers_.on('data', print);
+numbers_.on('end', function () {
+  console.log('numbers stream finished');
+});*/
+
+