I’ve started employing the import * as obj style within my tests, which imports all exports from a module as properties of an object which can then be mocked. I find this to be a lot cleaner than using something like rewire or proxyquire or any similar technique. I can’t speak for traceur which was … Read more
Yes, you can simplify to that, it’s totally safe. Sets and Maps are always iterated in insertion order Deleting an item does not affect the position of any iterator – you can visualise the shape of the collection not being changed, just being emptied. So: elements that are deleted and have not yet been iterated … Read more
When you need to import something that doesn’t export anything, but does something else, this is a side effect only module. You import it only to initialize it. Pure and Non Pure Modules If you think about modules as functions, a module that only effects the scope by exporting it’s content is like a function … Read more
It’s not an operator. In all senses of the word, it’s not one. It has been a huge misconception since it was introduced and despite popular opinion — it’s not one, and there are a few objective points to be made: It doesn’t fit the definition of an operator It can’t be used as an … Read more
change your code from: const local = this.props.local; to: const { local } = this.props; They are equivalent and you can call local.foo() in the same way. except that the second use object destructuring.
Declaring a variable as const requires you to immediately point it to a value and this reference cannot be changed. Meaning you cannot define it at one place (outside of try) and assign it a value somewhere else (inside of try). const test; // Syntax Error try { test = 5; } catch(err) {} On … Read more
In short: someValues.forEach((element) => { console.log(element); }); If you care about index, then second parameter can be passed to receive the index of current element: someValues.forEach((element, index) => { console.log(`Current index: ${index}`); console.log(element); }); Refer here to know more about Array of ES6: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
It helps to correctly import a default export in CommonJS/AMD/UMD module format. A default import (i.e. import d from “foo”) for a CommonJS/AMD/UMD module is equivalent to const d = require(“foo”).default But most of the CommonJS/AMD/UMD modules available today do not have a default export, making this import pattern practically unusable to import non-ES modules … Read more
Do let statements create properties on the global object? According to the spec, no: A global environment record is logically a single record but it is specified as a composite encapsulating an object environment record and a declarative environment record. The object environment record has as its base object the global object of the associated … Read more
Just check for varName === undefined. In older browsers it was possible to assign an alternate value to the global undefined variable causing that test to fail, but in ES2015+ that’s now impossible. Note that there’s no way to distinguish explicitly passing undefined as a parameter from leaving the parameter out altogether other than by … Read more