If you have a list of allowed values, you can easily retain them in an object using: const raw = { item1: { key: ‘sdfd’, value:’sdfd’ }, item2: { key: ‘sdfd’, value:’sdfd’ }, item3: { key: ‘sdfd’, value:’sdfd’ } }; const allowed = [‘item1’, ‘item3’]; const filtered = Object.keys(raw) .filter(key => allowed.includes(key)) .reduce((obj, key) => … Read more
A while ago our team migrated all its code (a mid-sized AngularJS app) to JavaScript compiled using Traceur Babel. I’m now using the following rule of thumb for functions in ES6 and beyond: Use function in the global scope and for Object.prototype properties. Use class for object constructors. Use => everywhere else. Why use arrow … Read more
The issue is with how ES6 modules are emulated in CommonJS how you import the module ES6 to CommonJS At the time of writing this, no environment supports ES6 modules natively. When using them in Node.js you need to use something like Babel to convert the modules to CommonJS. But how exactly does that happen? … Read more
Fundamentally WeakMaps provide a way to extend objects from the outside without interfering with garbage collection. Whenever you want to extend an object but can’t because it is sealed – or from an external source – a WeakMap can be applied. A WeakMap is a map (dictionary) where the keys are weak – that is, … Read more
What It Is This is an arrow function. Arrow functions are a short syntax, introduced by ECMAscript 6, that can be used similarly to the way you would use function expressions. In other words, you can often use them in place of expressions like function (foo) {…}. But they have some important differences. For example, … Read more
Node 13+ Since Node 13, you can use either the .mjs extension, or set {“type”: “module”} in your package.json. You don’t need to use the –experimental-modules flag. Modules is now marked as stable in node.js Node 12 Since Node 12, you can use either the .mjs extension, or set “type”: “module” in your package.json. And … Read more
According to MDN: A Map object can iterate its elements in insertion order – a for..of loop will return an array of [key, value] for each iteration. and Objects are similar to Maps in that both let you set keys to values, retrieve those values, delete keys, and detect whether something is stored at a … Read more
Update: See others answer, this is outdated. Short answer, no, there is no native support for private properties with ES6 classes. But you could mimic that behaviour by not attaching the new properties to the object, but keeping them inside a class constructor, and use getters and setters to reach the hidden properties. Note that … Read more
2018 update: There is now a stage 3 proposal – I am looking forward to make this answer obsolete in a few months. In the meantime anyone using TypeScript or babel can use the syntax: varName = value Inside a class declaration/expression body and it will define a variable. Hopefully in a few months/weeks I’ll … Read more
If you use Babel you can use the following syntax to copy property b from x into variable b and then copy rest of properties into variable y: let x = {a: 1, b: 2, c: 3, z:26}; let {b, …y} = x; and it will be transpiled into: “use strict”; function _objectWithoutProperties(obj, keys) { … Read more