How to test react hooks..? Is there any way to test react functions inside the components?
I researched many. But I couldn't find how to test react state changes(useState) and functions inside the components. How to test them?
I have a large React.js project, for which I have created separate SCSS files for separate React Components. The problem is styles in one component, let's say Component_1, are available in other components.
I have tried using import() the SCSS files within the Componets' componentWillMount() methods.
// instead of this
import "../Styles/_header.scss";
class Header extends React.Component {
// I am trying this
componentWillMount() {
import ("../Styles/_header.scss");
}
}
But I have many functional components, and for that I am seaching an Webpack way or any other way, so that my SCSS files will be only available in the Components from which I am importing... Thanks
I know it will have impact and you will need to refactor, but styled-components is your friend here.
Basically, you add styling on component level. In combination with lazy loading components you only load your component with its styling when the components need to be rendered by React.
You can use this babel plugin to conditionally import things. Also in your functional components you can use the effect hook to replace componentWillMount/componentDidMount.
I am writing the first applications in React Native. I'm using version 0.59. I imported the React-Navigation library and encountered the following problem:
I have a problem with the useEffect hook.When I next navigate to the component with useEffect I get following error : callback is not a function.
https://github.com/cassubianApp/react-navigation-test
it looks like the hook is calling, but right after that it gets a bug. Could this be a problem with my configuration or if React Navigation does not support hooks
Sorry for my english
I'm developing a React app using webpack and webpack-dev-server for development. However, all component life cycle methods (componentDidMount, componentWillMount etc.) other than getInitialState and render just don't work, while the components are rendered normally.
Example code:
https://gist.github.com/ryanaleksander/187308447d7665fd18aa1e6b8c5b656c
I have noticed that some of the places in articles they have used React.render() and some of the places ReactDOM.render(). Is there any specific difference between these two?
This is a very recent change introduced with 0.14. They split up React into a core library and the DOM adapter. Rendering is now done via ReactDOM.render.
https://facebook.github.io/react/blog/2015/10/07/react-v0.14.html
React.render has been deprecated as of React 0.14. With packages like react-native, react-art, react-canvas, and react-three, it is clear that the beauty and essence of React has nothing to do with browsers or the DOM.
To make this more clear and to make it easier to build more environments that React can render to, the main react package has been split into two: react and react-dom.
This paves the way to writing components that can be shared between the web version of React and React Native.
The react package contains React.createElement, .createClass, .Component, .PropTypes, .Children, and the other helpers related to elements and component classes. Think of these as the isomorphic or universal helpers that you need to build components.
The react-dom package has ReactDOM.render, .unmountComponentAtNode, and .findDOMNode.
React.render has been deprecated since React 0.14. React diverged into two separate libraries. The core library knows how to work with React components, nest them together and so on, but to take the component and render it to the DOM is a separate library called ReactDOM. So to render a component, you don't use React you use ReactDOM.
import React from 'react';
import ReactDOM from 'react-dom';
Then you would apply it like so:
ReactDOM.render(App);
If you try to run it like that, back then you would probably have gotten an error that says:
Invalid component element. Instead of passing a component class, make sure to instantiate it by passing it to React.createElement.
If you get that error, it's a bit cryptic, think of the following function below is creating an instance of a component to the DOM:
const App = function() {
return <div>Howdy!</div>;
}
I passed App as a class to ReactDOM.render() and not an instance of the component. So it's saying please ensure you make an instance of the component and then pass it, or we need to instantiate it and then pass it to the DOM.
So you would fix it by passing an instance like so:
ReactDOM.render(<App />);
So that would create an instance of App and pass it to ReactDOM.render() but you would not be quite there yet as you would probably have gotten the following error message:
Target container is not a DOM element.
So React is saying I am trying to render this but I don't know where to render it to because ReactDOM takes a second argument which is a reference to an existing DOM node on the page. When you render this <App /> component, insert that HTML into this element that already exists in our HTML document. You would go to your index.html file and find the div with class="container" or whatever it is and that is the root node. All we have to do is pass a reference to that container like so:
ReactDOM.render(<App />, document.querySelector('.container'));
Then you will get the component rendering to the screen. And lastly, five years ago we got ES6 syntax so that App component from above could be rewritten like so:
const App = () => {
return <div>Howdy!</div>;
}
So using a fat arrow like that is identical to using the function keyword.