Async Node.js solutions

data/lorem.txt

@@ -0,0 +1 @@
+Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod.

data/test.txt

@@ -0,0 +1 @@
+Hello!Hello again!

emitter.js

@@ -0,0 +1,32 @@
+var Emitter = function() {
+  this.listeners = {};
+
+  this.on = function(eventType, callback) {
+    if (this.listeners[eventType] === undefined) {
+      this.listeners[eventType] = [];
+    };
+    this.listeners[eventType].push(callback);
+  };
+
+  this.emit = function(eventType) {
+    var callbacks = this.events[eventType];
+    if (callbacks !== undefined) {
+      callbacks.forEach(function(callback) {
+        callback();
+      });
+    };
+  };
+
+  this.removeListener = function(eventType, callback) {
+    var i = this.listeners[eventType].indexOf(callback);
+    if (i !== -1) {
+      this.listeners[eventType].splice(i, 1);
+    };
+  };
+
+  this.removeAllListeners = function(eventType) {
+    delete this.listeners[eventType];
+  };
+};
+
+module.exports = Emitter;

file_io.js

@@ -0,0 +1,25 @@
+var fs = require('fs');
+
+var fsp = {
+  readFile: function(path) {
+    return new Promise(function(resolve, reject) {
+      fs.readFile(path, 'utf8', function(err, data) {
+        err ? console.error(err) : resolve(data);
+      });
+    });
+  },
+  writeFile: function(path, text) {
+    return new Promise(function(resolve, reject) {
+      fs.writeFile(path, text, 'utf8', function(err, data) {
+        err ? console.error(err) : resolve(fsp.readFile(path));
+      });
+    });
+  },
+  appendFile: function(path, text) {
+    return new Promise(function(resolve, reject) {
+      fs.appendFile(path, text, 'utf8', function(err, data) {
+        err ? console.error(err) : resolve(fsp.readFile(path));
+      });
+    });
+  }
+};

promises.js

@@ -0,0 +1,75 @@
+// 1.
+// var p = Promise.resolve('Hello Promise!');
+//
+// p.then(function(message) {
+//   setTimeout(function() {
+//     console.log(message);
+//   }, 1000);
+// });
+
+// 2.
+var delay = function(milliseconds) {
+  return new Promise(function(resolve, reject) {
+    setTimeout(function() {
+      resolve(milliseconds);
+    }, milliseconds);
+  });
+};
+
+var countDown = function(milliseconds) {
+  if (milliseconds > 0) {
+    console.log(milliseconds);
+    return delay(milliseconds - 100);
+  } else {
+    console.log('Done!');
+  };
+};
+
+// 3.
+var square = function(num) {
+  return new Promise(function(resolve, reject) {
+    if (typeof num === "number") {
+      resolve(num*num);
+    } else {
+      reject("Not a number");
+    };
+  });
+};
+
+var nums = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+nums = nums.map(function(i) {
+  return square(i);
+});
+
+Promise.all(nums)
+  .then(function(results) {
+    console.log(results);
+  }, function(err) {
+    console.error(err);
+  });
+
+// 4.
+var doBadThing = function(forRealz) {
+  return new Promise(function(resolve, reject) {
+    if (!forRealz) {
+      resolve("Yay!");
+    } else {
+      reject("Nay!");
+    };
+  });
+};
+
+doBadThing(true).then(function(result) {
+  console.log(result);
+}, function(err) {
+  console.error(err);
+});
+
+doBadThing(false)
+  .then(function(result) {
+    console.log(result);
+    throw "Error!";
+  })
+  .catch(function(err) {
+    console.error(err);
+  });