JavaScript Promise
Nothing weights lighter than a promise This maybe true regarding to human promises, however in the programming domain, promises are always kept. Following this optimistic note, today we'll be talking about JavaScript promises. Event Handling Problem Let's see what promises are good for and their basic capabilities starting with a problem they come to solve. Events are great for things of a repetitive nature like keydown , mousemove etc. With those events you don't really care about what have happened before you attached the listener. On contrary calling services and processing their response is a completely different kind of beast. Have a look at the following function, which reads a json file and returns it's content or an error in case of something goes wrong. function readJSON(filename, callback) { fs.readFile(filename, 'utf8', function (err, res) { if (err) { return callback(err); } try { res = JSON.parse(res);