ecmascript-next

I have tried searching through TypeScripts documentation on their configurtion and can't seem to find the answer to what should be a simple question. Simply, how does one configure the typescript compiler so that it knows what JavaScript feature sets we are using? So for example, ES2019 lands and i think 'Ohh want to get me some of that'. In that situation what do i need to upgrade, to allow the compiler to transpile and pollyfill what it needs to? The lib option in the tsconfig confuses me and the docs don't explain much about the available libraries. I can't find anything on them directly

Given var arr = [1,2,true,4,{"abc":123},6,7,{"def":456},9,[10]] we can filter number items within array arr using Number constructor var res = arr.filter(Number); // [1, 2, true, 4, 6, 7, 9, Array[1]] are true and [10] expected in resulting array ? If we substitute false for true at arr var arr = [1,2,false,4,{"abc":123},6,7,{"def":456},9,[10]] var res = arr.filter(Number) // [1, 2, 4, 6, 7, 9, Array[1]] using Array.isArray var res = arr.filter(Array.isArray) // [Array[1]] String var res = arr.filter(String) // [1, 2, true, 4, Object, 6, 7, Object, 9, Array[1]] If we want to filter items

Is there any reason to write classic syntax of ES6 methods? class MyClass { myMethod() { this.myVariable++; } } When I use myMethod() as callback on some event, I must write something like this (in JSX): // Anonymous function. onClick={() => { this.myMethod(); }} // Or bind this. onClick={this.myMethod.bind(this)} But if I declare method as arrow function: class MyClass { myMethod = () => { this.myVariable++; } } than I can write just (in JSX): onClick={this.myMethod} The feature you are using is not part of ES6. It's the class fields proposal . It allows you to initialize instance properties

I have to pass a function to another function, and execute it as a callback. The problem is that sometimes this function is async, like: async function() { // Some async actions } So I want to execute await callback() or callback() depending on the type of function that it is receiving. Is there a way to know the type of the function?? Native async functions may be identifiable when being converted to strings : asyncFn[Symbol.toStringTag] === 'AsyncFunction' Or by AsyncFunction constructor: const AsyncFunction = (async () => {}).constructor; asyncFn instanceof AsyncFunction === true This won't

I am using ReactJS with Babel and Webpack and using ES6 as well as the proposed class fields for arrow functions. I understand that arrow functions make things more efficient by not recreating the functions each render similar to how binding in the constructor works. However, I am not 100% sure if I am using them correctly. The following is a simplified section of my code in three different files. My code: Main.js prevItem = () => { console.log("Div is clicked") } render(){ return ( <SecondClass prevItem={this.prevItem} /> ) } SecondClass.js <ThirdClass type="prev" onClick={()=>this.props

Take the following loop: for(var i=0; i<100; ++i){ let result = await some_slow_async_function(); do_something_with_result(); } Does await block the loop? Or does the i continue to be incremented while await ing? Is the order of do_something_with_result() guaranteed sequential with regard to i ? Or does it depend on how fast the await ed function is for each i ? Does await block the loop? Or does the i continue to be incremented while await ing? "Block" is not the right word, but yes, i does not continue to be incremented while awaiting. Instead the execution jumps back to where the async