ecmascript-6 – Page 57

How to assign the correct typing to React.cloneElement when giving properties to children?

December 26, 2022 by Tarik

The problem is that the definition for ReactChild is this: type ReactText = string | number; type ReactChild = ReactElement<any> | ReactText; If you’re sure that child is always a ReactElement then cast it: return React.cloneElement(child as React.ReactElement<any>, { width: this.props.width, height: this.props.height }); Otherwise use the isValidElement type guard: if (React.isValidElement(child)) { return React.cloneElement(child, … Read more

What does the Reflect object do in JavaScript?

December 26, 2022 by Tarik

UPDATE 2015: As pointed out by 7th’s answer, now that ES6 (ECMAScript 2015) has been finalized, more appropriate documentation is now available: ES6 spec, Reflection MDN Reflect (including details and examples to all of its methods) **Original answer (for (historic) understanding and extra examples)**: The Reflection proposal seems to have progressed to the Draft ECMAScript … Read more

ES6 Object Destructuring Default Parameters

December 26, 2022 by Tarik

Yes. You can use “defaults” in destructuring as well: (function test({a = “foo”, b = “bar”} = {}) { console.log(a + ” ” + b); })(); This is not restricted to function parameters, but works in every destructuring expression.

How do I fix “Expected to return a value at the end of arrow function” warning?

December 25, 2022 by Tarik

A map() creates an array, so a return is expected for all code paths (if/elses). If you don’t want an array or to return data, use forEach instead.

Promises, pass additional parameters to then chain

December 25, 2022 by Tarik

Perhaps the most straightforward answer is: P.then(function(data) { return doWork(‘text’, data); }); Or, since this is tagged ecmascript-6, using arrow functions: P.then(data => doWork(‘text’, data)); I find this most readable, and not too much to write.

ES6 export default with multiple functions referring to each other

December 25, 2022 by Tarik

The export default {…} construction is just a shortcut for something like this: const funcs = { foo() { console.log(‘foo’) }, bar() { console.log(‘bar’) }, baz() { foo(); bar() } } export default funcs It must become obvious now that there are no foo, bar or baz functions in the module’s scope. But there is … Read more

Unexpected comma using map()

December 25, 2022 by Tarik

Explanation template literals use the toString() method which by default joins the returned array by map with a ,. To avoid this “problem” you can use join(”) Code var description = [ ‘HTML & CSS’, ‘Javascript object-oriented programming’, ‘Progressive Web apps (PWAs)’, ‘Website Performance Optimization’, ‘Webpack and Gulp workflows’, ‘Fullstack React.js’, ‘Web Components’, ‘Responsive web … Read more

Debugging in Safari’s Web Inspector, when using a module loader like SystemJS

December 24, 2022 by Tarik

Well, maybe you can use some IDE like WebStorm with a strong Debugger for Web and Node. Examples: You can see more about WebStorm debugger here. Some alternatives for WebStorm: Atom (Free) Intellij IDEA (community: Free) Visual Studio Code (Free) … P.S: I develop Ionic and React apps with WebStorm 😀

Does ES6 module importing execute the code inside the imported file?

December 24, 2022 by Tarik

Yes, it does, exactly one time. See http://www.ecma-international.org/ecma-262/6.0/#sec-abstract-module-records: Do nothing if this module has already been evaluated. Otherwise, transitively evaluate all module dependences of this module and then evaluate this module

Why do arrow functions not have the arguments array? [duplicate]

December 24, 2022 by Tarik

Arrow functions don’t have this since the arguments array-like object was a workaround to begin with, which ES6 has solved with a rest parameter: var bar = (…arguments) => console.log(arguments); arguments is by no means reserved here but just chosen. You can call it whatever you’d like and it can be combined with normal parameters: … Read more