JavaScript ES6 default imports vs named imports

I’d been wondering this for a while. What’s the difference between this style of ES6 import:

import A from './A';


import { A } from './A';

I’ve seen and used both, and had guessed that the { A } syntax is when you’re importing a specific named function from a module? I wasn’t convinced this was correct. It turns out the difference is importing a default export, versus importing using a named import.

This is explained here this SO post here:

Adding react-bootstrap to a React app

Adding Bootstrap to an existing or new React app is not as obvious or easy as you would think, because of Bootstrap’s dependencies on other libraries, like jQuery (and see answers to Quora question here).

The react-bootstrap module is a React specific implementation of Bootstrap that provides JSX components for a number of the Bootstrap provided styles and components, and even layout CSS encapsulated as JSX components like: <Grid>, <Row> and <Col>

Installing it via npm is as simple as:

npm intall --save react-boostrap

You then import what you need from the module like:

import {Bootstrap, Grid, Row, Col} from 'react-bootstrap';

and then you quickly discover that the CSS based layout is not working like you’d expect. If you check the Getting Started section it mentions:

Because React-Bootstrap doesn’t depend on a very precise version of Bootstrap, we don’t ship with any included css. However, some stylesheet is required to use these components. How and which bootstrap styles you include is up to you, but the simplest way is to include the latest styles from the CDN.

Ok. So you can follow their example and load from the Bootstrap (or other) CDN, but what if you want to manage Bootstrap as an npm module too? This question is answered in this post here. What you need is to install bootstrap:

npm install --save bootstrap

and then include it into your main App.jsx with:

import 'bootstrap/dist/css/bootstrap.css';
import 'bootstrap/dist/css/bootstrap-theme.css';

and you’re up and running. Not that obvious but once you’ve setup this once, probably makes more sense the next time.

React: ‘Element type is invalid … check your render method’

Once you’ve seen this error once in your React app you’ll probably instantly recognize it and know exactly what this means:

Uncaught Error: Element type is invalid: expected a string 
(for built-in components) or a class/function (for composite 
components) but got: object. You likely forgot to export your 
component from the file it's defined in. Check the render 
method of `App`.

The key is “You likely forgot to export your component…” which was exactly the issue in my case.

If you have an ES6 style component this:

class App extends Component {

… check that you’ve exported it at the end of the source file with:

export default App;

Appending values to the end of a file from a Unix shell

Some things you do repeatedly from a *nix shell are incredibly useful and time-saving that you do them without thinking about it. Say for example you need to add a file or directory name to a file like .gitignore. On Windows you might open an editor and add the new lines to the end of the file and save it, but in a *nix shell (I imagine there’s a comparable approach maybe using something like Windows Powershell too), you can do:

echo "newfile" >> .gitignore

and you’re done.