Iterating over an array using for…in doesn’t guarantee order, however ES6 introduces a new construct for…of. My limited testing of implementations of for…of indicates that it does iterate in order on array, but is this property guaranteed? Yes, the order of for-of on arrays is guaranteed by the array iterator definition: It will visit the … Read more
Yes, it is possible from jest@25.4.0. From this version, there is a native support of esm, so you will not have to transpile your code with babel anymore. It is not documented yet, but according to this issue you have to do 3 easy steps to achieve that (At the time of writing this answer): … Read more
Your update function would look like this updateItem(id, itemAttributes) { var index = this.state.items.findIndex(x=> x.id === id); if (index === -1) // handle error else this.setState({ items: [ …this.state.items.slice(0,index), Object.assign({}, this.state.items[index], itemAttributes), …this.state.items.slice(index+1) ] }); } And you use it like this this.updateItem(2, {someattr: ‘a new value’}); Gross right? You’re going to have a big … Read more
Like (almost) any tool ‘/x’ means ‘x’ in the root of your filesystem. Babel doesn’t actually look at the paths, it just compiles import {myFunc} from ‘/my-module’; into var _myModule = require(‘/my-module’); And node actually looks up the module. If you really want to import relative to the root of the project, you could use … Read more
That is not valid syntax. You can do export { Post } or even just export var Post = Parse.Object.extend(‘Post’) or shorten the whole file to export default Parse.Object.extend(‘TestObject’) export var Post = Parse.Object.extend(‘Post’) Your imports are also incorrect, you’ll want to do import TestObject, { Post } from ‘../store’ This is if you really … Read more
Per the Redux FAQ question at here, this.props.dispatch is available by default if you do not supply your own mapDispatchToProps function. If you do supply a mapDispatchToProps function, you are responsible for returning a prop named dispatch yourself: const mapDispatchToProps = dispatch => ({ …other methods, dispatch // ← Add this }) export default connect(null, … Read more
Your specific example is: data.map(users => { console.log(users); }); Where data is the following array: [ {id: 1, username: “Foo”}, {id: 2, username: “Bar”}, ] data.map function (check Array.prototype.map specification) converts one array (data in your case) to a new array. The conversion (mapping) is defined by the argument of data.map, also called the callback … Read more
If your question is “why does response.json() return a promise?” then @Bergi provides the clue in comments: “it waits for the body to load”. If your question is “why isn’t response.json an attribute?”, then that would have required fetch to delay returning its response until the body had loaded, which might be OK for some, … Read more
Isn’t there a .always like jQuery has? No, there’s not (yet). Though there is an active proposal, so maybe ES2018. Yes, there is: promise .finally() is part of the standard since ES2018. If not, how do I achieve this? You can implement the finally method yourself like this: Promise.prototype.finally = function(cb) { const res = … Read more
Why is the “this” inside of of the Clickers’ click method referring to the dom node rather than … itself? Because the specification for .addEventListener() is to set the this pointer to the DOM element that caught the event. That’s how it is designed to work. When passing a method as a callback where you … Read more