arrow-functions

This question already has an answer here: ECMAScript 6 arrow function that returns an object 6 answers According to the documentation , you can return an expression from an arrow function: (param1, param2, …, paramN) => expression // equivalent to: => { return expression; } but this doesn't seem to work as I would expect (nodejs 4.2.3) > [1,2,3].map(i => i); [ 1, 2, 3 ] > [1,2,3].map(i => {}); [ undefined, undefined, undefined ] Shouldn't the 2nd example return 3 empty objects? Or am I missing something? According to the docs , the body of fat arrow function can be written as either a single

I have just been schooled on arrow functions, and how they can aid with visibility when you start using sub-functions, here: react native and globally accessible objects I am not sure if this is different for "if" statements, but I can't get this to work at all. The issue: myFunction() { console.log('Welcome Flag: ' + this.props.welcomeFlag); if (this.props.welcomeFlag == false) { this.props.dispatch(setWelcomeFlag(true)); showMessage('Welcome back, ' + this.props.userName + '!', { duration: 3000 }); } } In this example, the console logs the initial value of welcomeFlag, which is "false". I

The title says it all. When I use the fat-arrow in CoffeeScript, it stores this first before calling the function. For example: class myClass constructor: -> element = $ "#id" element.click -> @myMethod(@value) return return myMethod: (c)-> window.console.log(c) return would yield var myClass; myClass = (function() { function myClass() { var element; element = $("#id"); element.click(function() { this.myMethod(this.value); }); return; } myClass.prototype.myMethod = function(c) { window.console.log(c); }; return myClass; })(); Now on line#8 of JavaScript, this.myMethod is wrong. In this scope,

I try to understand arrow functions of typescript by the example of Angular 2 Observable subscribe method. Could somebody explain me: I have this code which works: this.readdataservice.getPost().subscribe( posts => { this.posts = posts; } ); but should it be the same if I use this? But this doesn't work. this.readdataservice.getPost().subscribe( function (posts) { this.posts = posts; } ); JS by default executes functions in the scope of the caller. If you pass a function around to be called somewhere else, this points to the caller. In your code you pass the function to the observable via the

I'm having some issues understanding why I'm getting a compile warning on this piece of my react code fetch('/users') .then(res => res.json()) .then(data => { data.map(users => { console.log(users); }); }); The warning I'm getting is Expected to return a value in arrow function array-callback-return However I'm still get the json object values from my /users , and they are printed to the console individually. The object is: { id: 1, username: "Foo" }, { id: 2, username: "Bar" } Am I missing a return statement, or am I missing something with how map returns values after a .then() ? I'm unclear

How to using ES6 Arrow function to realize IIFE Immediately-Invoked Function Expression ? Here is my demo codes, and it had tested passed! // ES 6 + IIFE (() => { let b = false; console.log(`b === ${b}!`); const print = `print()`; if(window.print){ b = true; console.log(`b === ${b}!`); } let x = () => { if(b){ console.log(`Your browser support ${print} method.`); }else{ alert(`Your browser does not support ${print} method.`); console.log(`Your browser does not support ${print} method.`); }; } x(); })(); const dcs = `IIFE: Douglas Crockford's style`; // ES 5 + IIFE is OK (function(){ alert(

Given class BaseClass{ count:number=0; public someMethod=():void =>{ this.count++; } } class ChildClass extends BaseClass{ public someMethod=():void=>{ super.someMethod(); //Do more work here. } } I receive the error message: Only public methods of the base class are accessible via the 'super' keyword. @Basarat provides some information here but this seems like a real hack to the language. typescript arrow operator to define a function on prototype How might this be done while preserving contextual use of 'this'? Am I using arrow functions properly or should they really only be used as a

I'm currently implementing the static land specification (an alternative of fantasy land). I want to not only use plain objects as types but also ES2015 classes with static methods. I've implemented these static methods as arrow functions in curried form instead of normal functions. However, this isn't possible with ES2015 classes: class List extends Array { static map = f => xs => xs.map(x => f(x)) static of = x => [x] } My map doesn't need its own this , because it is merely a curried function on the List constructor. To make it work I have to write static map(f) { return xs => xs.map(x => f