ecmascript-7

There are already a lot of cool features in ES6/ES7 for defining Javascript objects. However, the following pattern is common in Javascript: const obj = { requiredKey1: ..., requiredKey2: ... }; if (someCondition) { obj.optionalKey1 = ...; } Is there a way to define the object all at once with both optional and required keys? You can use object spread to have an optional property. Note: Object Rest/Spread is a stage 4 proposal for ECMAScript. You might need the babel transform to use it. let flag1 = true; let flag2 = false; const obj = { requiredKey1: 1, requiredKey2: 2, ...(flag1 && {

Do you know if it is possible to get the array of interfaces implemented by a class using a decorator: interface IWarrior { // ... } interface INinja { // ... } So If I do something like: @somedecorator class Ninja implements INinja, IWarrior { // ... } At run-time Ninja will have an annotation which contains ["INinja", "IWarrior"] ? Thanks Currently, types are used only during development and compile time. The type information is not translated in any way to the compiled JavaScript code. But you however can pass the list of strings to the decorator parameter like this: interface IWarrior { //

I'm trying to check if the user with the email provided exists in the collection users , but my function keeps returning undefined for every call. I use es6 and async/await in order to get rid of lots of callbacks. Here's my function (it is inside of a class): async userExistsInDB(email) { let userExists; await MongoClient.connect('mongodb://127.0.0.1:27017/notificator', (err, db) => { if (err) throw err; let collection = db.collection('users'); userExists = collection.find({email: email}).count() > 0; console.log(userExists); db.close(); }); console.log(userExists); return userExists; } So,

I've just discovered the ECMAScript 7 feature a**b as an alternative for Math.pow(a,b) ( MDN Reference ) and came across a discussion in that post , in which they apparently behave differently. I've tested it in Chrome 55 and can confirm that the results differ. Math.pow(99,99) returns 3.697296376497263e+197 whereas 99**99 returns 3.697296376497268e+197 So logging the difference Math.pow(99,99) - 99**99 results in -5.311379928167671e+182 . So far it could be said, that it's simply another implementation, but wrapping it in a function behaves different again: function diff(x) { return Math.pow

I am in the process of writing my first Koa.js app, and having recently been introduced to the ES2016 (aka ES7) features of async / await , I wanted to make use of these. I found that my Google skills were not up to the task, and the few snippets of code I could find were either for the standard Koa (using generators) or otherwise not-as-bleeding-edge-as-ES7. See my answer below for how I got my tests running. I'm still a beginner, so it's likely that a lot of this can be optimised considerably, but here's what worked for me. I'll basically just dump my files here, they should be fairly

I stuck with this bit and I can't progress - I guess solution is simple but I can't figure out. I'm trying to add entry in reducer so data in in would look something this: state = { entryId: { entryName: ["something", "something2", "something3" /* and so on... */] } }; So far this is the closest I get, but, instead of adding new unique entry, it is replacing the one that is stored already. Also I need to be able to add this item to empty state where entryId, entryName doesn't exist yet to avoid error: switch(type) { case ADD_ENTRY: return { ...state, [entryId]: { ...state[entryId], [entryName]