Immediately, yes, by specification. From the MDN: The executor function is executed immediately by the Promise implementation, passing resolve and reject functions (the executor is called before the Promise constructor even returns the created object) This is defined in the ECMAScript specification (of course, it’s harder to read…) here (Step 9 as of this edit, showing … Read more
The problem is that you are not returning anything from inside the innermost map function. return Object.keys(secondData).map((thirdData, i) => { return <div key={i}> {this.thirdData(thirdData)} </div> } P.S. Make sure you assign unique keys to iterator as well One thing to note here is the difference between () => {} and () => (…), in the … Read more
If you want to display a sort of confirmation before leaving the page then follow the beforeunload event guidelines According to the specification, to show the confirmation dialog an event handler should call preventDefault() on the event. However note that not all browsers support this method, and some instead require the event handler to implement … Read more
You could reverse the comparison (equal instead of unqual) and return the negated result of some. const array1 = [{ id: 1 }, { id: 2 }, { id: 3 }, { id: 4 }], array2 = [{ id: 1 }, { id: 3 }], array3 = array1.filter(entry1 => !array2.some(entry2 => entry1.id === entry2.id)); // … Read more
The closest I can come up with is: var { iWantThis, iWantThis: { andThis, andThisToo } } = x; Though I’d use let instead, if I’m using ES6 😉
But what if the array has 100 items and I want the 99’th age ? Arrays are objects, so this will do: let {title: lectureTitle, topics: {98: {age: thirdAge}}} = lecture; Note however that the […] type of destructuring works with any iterable, whereas {…} only works with objects (and therefore arrays). For the above … Read more
The relevant specs are here: Promises/A+ point 2.2.4: onFulfilled or onRejected must not be called until the execution context stack contains only platform code. [3.1]. And note 3.1 (emphasis mine): Here “platform code” means engine, environment, and promise implementation code. In practice, this requirement ensures that onFulfilled and onRejected execute asynchronously, after the event loop … Read more
Whenever you’re looking for reducing an array of values to one value, you’re looking for .reduce(): state = { fields: fields.reduce((acc, key) => ({…acc, [key]: ”}), {}), };
If you don’t care about the results, then it’s quick to whip one up: Promise.eachLimit = async (funcs, limit) => { let rest = funcs.slice(limit); await Promise.all(funcs.slice(0, limit).map(async func => { await func(); while (rest.length) { await rest.shift()(); } })); }; // Demo: var wait = ms => new Promise(resolve => setTimeout(resolve, ms)); async function … Read more
Apparently, ES6 doesn’t need namespacing because each file is a separate module. Not exactly. Each module does have its own scope, that is correct, but not every file is a module. There still are scripts in ES6 that work just like those from ES5, and are executed in the global scope. In those scripts, you … Read more