Using Create-react-app, I want to lazy load some of my components, this is working fine as long as the components are in the same folder as my main component (where I define the routes) however as soon as I want to load a component from another folder like
loader: () => import("../containers/HomeAContainer")
it fails to find/import the module. (exact same module will work if I move the file!
I have made a complete example which can be seen here
I have also tried to change the route to src/x/x instead of ../x/x but again getting errors.
You are using a wrong path, correct it by using :
{ path: "/c", component: "./containers/HomeAContainer" }
The way i create lazy loading components is through a higher order component. I create a file called "asyncComponent", then i put in the code:
import React, { Component } from 'react';
const asyncComponent = ( importComponent ) => {
return class extends Component{
state = { component: null }
componentDidMount(){
importComponent().then(cmp =>{
this.setState({component: cmp.default});
});
}
render (){
const C = this.state.component;
return C ? <C {...this.props} /> : null;
}
}
}
export default asyncComponent;
This component will receive a function as a parameter and then return the component you want. The function is actually a import funcion with the path of your component that you want to lazy load.
So instead of using:
import Exemple from './example/example';
You will use:
import asyncComponent from './asyncComponent';
const asyncExample = asyncComponent(()=>{
return import('./example/example');
});
Related
I have a path.json file that contains the path of a component
// path.json
{
"main": "./login/index.js",
"paths": [
{
"name": "login",
"path": "./login/index.js",
"image": ""
}
]
}
I want to load './login/index.js' file dynamically in react native and render this particular file
My current implementation
const MyComponent = createLazyContainer(() => {
const componentPath = PathJson.main; // ./login/index.js
return import(`${componentPath}`); //import error here # line 7
});
export default MyComponent;
I am getting following error :
Invalid call at line 7: import("" + componentPath)
What people have been telling you in the thread is correct but I'd like to add one possible solution. All the imports/require are resolved at compilation time and not at running time which you are trying to do. By the time you are running your app, if you haven't imported the files, you can't use them.
There is a workaround tho, assuming that you know all the files that you might in advance which is to do something like a factory:
const possiblePaths = {
'one': require('path/to/file/1'),
'two': require('path/to/file/2')
}
function(type){
return possiblePaths[type];
}
And then you use it somehow like:
render(){
const MyComponent = function('one');
return <MyComponent/>;
}
This is more or less pseudo code and my not work right away, but hopefully yo get the idea. You need to store a reference to each of the imports you might need and then dont use the import, use the reference that was created for you at compilation time.
Actually, the React Native development concerns are not like development for the Web.
Just for this reason, it is not so important at all to have lazy loading in the production of a react-native project. Just import anything you want and then use them in any files of the project. all of them are in the bundle of production and exactly it is not important at all.
So for this problem, I prefer to have a helper file to collect all selectable libraries and export them:
// helper file
export { default as Index } from './Login';
export { default as OtherComponent } from './OtherComponent';
Then when you wanna use:
import { Index, OtherComponent } from 'helper';
~~~
render() {
const MyComponent = someCondition ? Index : OtherComponent;
return (
<MyComponent />;
);
}
Solution:
const allPaths = {
path1: require('file path1').default,
path2: require('file path2').default
};
render(){
const MyComponent = allPaths["path1"];
return <MyComponent/>
}
In React Native all the files that are being imported are bundled together, only those files can be dynamically imported.
Let's say you have three files index.js, test_1.js and test_2.js and if you have imported only test_1.js in index.js than React Native will only bundle those two files leaving test_2.js.
So to answer your question even if dynamic import works in React Native but because these files are not part of the bundle you are not able to import them.
I've once been in a similar situation where I need to do imports by variable, but that is limited to importing components inside a component and it uses code-splitting (Edit: I'm playing around to look for a solution without relying on code-splitting, I just realized there was a react-native tag in the question, and I don't think code-splitting is a good choice to go with in RN). I'm not sure by how much my method could help you, but here goes.
Side notes:
Importing folder that contains an index.js(jsx|ts|tsx) file should automatically resolve to that index file.
Importing from from './login/index.js' usually throws a 'Module not found' error. Either import from './login/index' or from './login but I prefer the last one as it's the shortest & simplest.
In path.json:
{
"main": "./login", // '.js' is removed
"paths": [
{
"name": "login",
"path": "./login/index.js", // Not sure what this is for, but if necessary, remove the '.js' here as well
"image": ""
}
]
}
In MyComponent.js:
import React, { lazy, Suspense } from 'react'
import PathJson from './path'
// 1. We need a UI to show while component is being loaded
const Loader = () => <div>{'Loading...'}</div>
// 2. We need a fallback UI if component is not found
const DocUnavailable = () => <div>{'We\'re sorry, but this document is unavailable.'}</div>
// 3. Create a resolver function ('resolver' is just a name I give)
function resolveImport(pathToComponent, FallbackComponent) {
let componentFound = false
let RenderComponent = () => <FallbackComponent /> // Assign fallback first
try {
if (require.resolve(pathToComponent)) {
componentFound = true
}
} catch (e) { } // Kinda hacky, if you don't mind, but it works
if (componentFound) {
// If found, replace fallback with the valid component
RenderComponent = lazy(() => import(pathToComponent))
}
return RenderComponent
}
// 4. Finally, implement it in a component
class MyComponent extends React.Component {
render() {
const componentPath = PathJson.main
const RenderComponent = resolveImport(componentPath, DocUnavailable)
return (
<Suspense fallback={<Loader />}>
<RenderComponent />
</Suspense>
)
}
}
export default MyComponent
References:
Implementation for 'resolver' function based on Langutil
Code-splitting with lazy & Suspense based on React Docs
Trying next with layout pattern:
https://github.com/zeit/next.js/tree/canary/examples/layout-component
And the problem is that Layout component get remounted on every page change. I need to use layout component as a Container so it'll fetch data from server on every mount. How can I prevent layout to get re-mounted? Or am I missing something there?
This helped me for persistent layouts. The author puts together a function that wraps your page components in your Layout component and then passes that fetch function to your _app.js. This way the _app.js is actually the components that renders the Layout but you get to specify which pages use which layout (in case you have multiple layouts).
So you have the flexibility of having multiple layouts throughout your site but those pages that share the same layout will actually share the same layout component and it will not have to be remounted on navigation.
Here is the link to the full article
Persistent Layout Patterns in Next.js
Here are the important code snippets. A page and then _app.js
// /pages/account-settings/basic-information.js
import SiteLayout from '../../components/SiteLayout'
import AccountSettingsLayout from '../../components/AccountSettingsLayout'
const AccountSettingsBasicInformation = () => (
<div>{/* ... */}</div>
)
AccountSettingsBasicInformation.getLayout = page => (
<SiteLayout>
<AccountSettingsLayout>{page}</AccountSettingsLayout>
</SiteLayout>
)
export default AccountSettingsBasicInformation
// /pages/_app.js
import React from 'react'
import App from 'next/app'
class MyApp extends App {
render() {
const { Component, pageProps, router } = this.props
const getLayout = Component.getLayout || (page => page)
return getLayout(<Component {...pageProps}></Component>)
}
}
export default MyApp
If you put your Layout component inside page component it will be re-remounted on page navigation (page switch).
You can wrap your page component with your Layout component inside _app.js, it should prevent it from re-mounting.
Something like this:
// _app.js
import Layout from '../components/Layout';
class MyApp extends App {
static async getInitialProps(appContext) {
const appProps = await App.getInitialProps(appContext);
return {
...appProps,
};
}
render() {
const { Component, pageProps } = this.props;
return (
<Layout>
<Component {...pageProps} />
<Layout />
);
}
}
export default MyApp;
Also, make sure you replace all the to <Link href=""></Link>, notice that only have change the Html tag to link.
I struggled because with this for many days, although I was doing everything else correctly, these <a> tags were the culprit that was causing the _app.js remount on page change
Even though this is the topic Layout being mounted again and again, the root cause of this problem is that you have some data loaded in some child component which is getting fetched again and again.
After some fooling around, I found none of these problem is actually what Next.Js or SWR solves. The question, back to square one, is how to streamline a single copy of data to some child component.
Context
Use context as a example.
Config.js
import { createContext } from 'react'
export default createContext({})
_App.js
import Config from '../Config'
export default function App({ Component, pageProps }) {
return (
<Config.Provider value={{ user: { name: 'John' }}}>
<Component {...pageProps} />
</Config.Provider>
)
}
Avatar.js
import { useContext } from 'react'
import Config from '../Config'
function Avatar() {
const { user } = useContext(Config)
return (
<span>
{user.name}
</span>
)
}
export default Avatar
No matter how you mount and dismount, you won't end up with re-render, as long as the _app doesn't.
Writable
The above example is only dealing with readable. If it's writable, you can try to pass a state into context. setUser will take care the set in consumer.
<Provider value={useState({})} />
const [user, setUser] = useContext(Config)
setUser is "cached" and won't be updated. So we can use this function to reset the user anytime in child consumer.
There're other ways, ex. React Recoil. But more or less you are dealing with a state management system to send a copy (either value or function) to somewhere else without touching other nodes. I'll leave this as an answer, since even we solved Layout issue, this problem won't disappear. And if we solve this problem, we don't need to deal with Layout at all.
I am trying to use react-loadable on third party react components. It is just showing blank page. When I used it to code split my own components, it worked fine.
import React from 'react'
import Loadable from 'react-loadable';
const Loading = () => <div>Loading...</div>
const Modal = Loadable({
loader: () => import('react-responsive-modal'),
/*loader: () => import('./My-Own-Component'),//this works fine.*/
loading: Loading
});
class MyTest extends React.Component{
render(){
return(<Modal />)
}
}
export default MyTest
I am sure the way I am using is wrong. Please advise. Thanks.
Just a hunch. Can you try extracting the component inside react-responsive-modal into a custom component and try to see if that works.
I think React loadable is not able to import 3rd party components directly.
I'm developing an application using create-react-app and I'm trying to split my code into modules implementing the way described in the react-router huge-apps example.
Everything works well except the unit tests : I get this error while running the jest tests for the route components :
TypeError: Cannot read property 'contextTypes' of undefined
A route component looks like this :
export class IntroPage extends React.Component {
render() {
return (
<div></div>
);
}
}
const mapStateToProps = (state) => {
return {
...
}
};
module.exports = connect(mapStateToProps)(IntroPage);
and a test :
import React from 'react';
import {shallow} from 'enzyme';
import {IntroPage} from '../IntroPage';
it('should render without crashing', () => {
shallow(
<IntroPage {...props}/> // IntroPage is undefined
)
});
How do I have to export/import my components to be able to test them properly.
Thanks.
If you transpile in Babel:
export class IntroPage extends React.Component {
...
}
You will notice that Babel will move that to the exports variable.
Object.defineProperty(exports, "__esModule", {
value: true
});
... more good stuff
...
var IntroPage = exports.IntroPage = function (_React$Component) {
So you can console.log these:
console.log(exports);
console.log(module.exports);
console.log(module);
and check exports variable and module object.
In here module.exports should be the same as exports.
If you type:
module.exports = connect(mapStateToProps)(IntroPage);
at the end of your component file, you are overwriting the module.exports with the new value.
This is the core of the problem.
The solution?
I think you already found one, but the best would be not to mix commonJS with ES6 export, since ES6 export will be transpiled to commonJS syntax.
Check also "What is export default in JavaScript?"
Found a solution with this post : React router dynamic routes not rendering component
I just had to add 'default' to the require statements when exporting with es6 module.
I have a redux reducer loaded with several reactjs components.
I want to load these inside other components through this.props
Like: this.props.components.MyReactComponent
class OtherComponent extends Component {
render() {
const Component = this.props.components.MyReactComponent
return (
<div>
<Component />
</div>
)
}
}
Is this possible? If so, how?
EDIT The component is a connected component. I am able to load it but it is broken. In this case, it is a counter, when you click to increment or decrement nothing happens. In the console, there is this error:
Uncaught ReferenceError: _classCallCheck is not defined
if I convert the component into a dumb component (without connecting it), the error is this:
Uncaught ReferenceError: _classCallCheck3 is not defined
EDIT 2
I found out why those errors show up. It is because the react component gets stripped out when stored in the reducer:
A react component would look something like this:
{ function:
{ [Function: Connect]
displayName: 'Connect(Counter)',
WrappedComponent: { [Function: Counter] propTypes: [Object] },
contextTypes: { store: [Object] },
propTypes: { store: [Object] } } }
However, after I store it inside a reducer, it loses its properties and ends up looking something like this:
{ function:
{ [Function: Connect] } }
After reading the comments below, I thought of an alternative. I can store in a reducer the path to each component, then make a new wrapper component that could render those other components from those paths.
I tried it but encoutered a different problem with the funcion require from nodejs that for some weird reason is not letting me user a variable as an argument. For example:
This works:
var SomeContent = require('../extensions/myContent/containers')
This does not:
var testpath = '../extensions/myContent/containers'
var SomeContent = require(testpath)
Giving me the following error:
Uncaught Error: Cannot find module '../extensions/myContent/containers'.
It is adding a period at the end of the path. How can I prevent require to add that period?
If you can think of any other alternative I can implement for what I am trying to do, I would greatly appreciate it.
EDIT 3 Following Thomas advice...
What I am trying to accomplish is this:
I want to be able to render react components inside other react components, I know how to do it the same way most us know how to; however, I want to be able to do it by importing a file that would contain all the components without actually having to import and export each one of them:
OtherComponent.js
import React, { Component } from 'react'
import { SomeComponent } from '../allComponentes/index.js'
export default class OtherComponent extends Component {
render() {
return (
<SomeComponent />
)
}
}
SomeComponent.js
import React, { Component } from 'react'
export default class SomeComponent extends Component {
render() {
return (
<div>
Hello
</div>
)
}
}
allComponents/index.js
import SomeComponent from '../allComponents/SomeComponent/index.js'
export { SomeComponent }
What I am trying to do in allComponents/index.js is to avoid having import/export statements for each component by reading (with fs module) all the components inside the allComponents folder and export them.
allComponents/index.js (pseudocode)
get all folders inside allComponents folder
loop through each folder and require the components
store each component inside an object
export object
When I tried that, I encountered multiple issues, for one, export statements have to be in the top-level, and second, fs would work only on the server side.
So, that is why I thought of loading all the components in a reducer and then pass them as props. But as I found out, they got stripped out when stored them in a reducer.
Then, I thought of only storing the path to those components inside a reducer and have a wrapper component that would use that path to require the needed component. This method almost worked out but the nodejs function require wont allow me to pass a variable as an argument (as shown in EDIT 2)
I think your question is not really to do with redux but rather is (as you say):
What I am trying to do in allComponents/index.js is to avoid having import/export statements for each component by reading (with fs module) all the components inside the allComponents folder and export them.
By way of example, I have all of my (dumb) form components in a folder path components/form-components and the index.js looks something like:
export FieldSet from './FieldSet'
export Input from './Input'
export Label from './Label'
export Submit from './Submit'
export Select from './Select'
export Textarea from './Textarea'
Then when I want to import a component elsewhere, it is import { FieldSet, Label, Input, Submit } from '../../components/form-components/';