How to declare a global variable in React?
ReactjsJavascript GlobalizeReactjs Problem Overview
I initialized i18n
translation object once in a component (a first component that loads in the app ). That same object is required In all other components. I don't want to re-initialize it in every component. What's the way around? Making it available to window scope doesn't help as I need to use it in the render()
method.
Please suggest a generic solution for these problems and not i18n specific solution.
Reactjs Solutions
Solution 1 - Reactjs
Beyond React
You might not be aware that an import is global already. If you export an object (singleton) it is then globally accessible as an import statement and it can also be modified globally.
If you want to initialize something globally but ensure its only modified once, you can use this singleton approach that initially has modifiable properties but then you can use Object.freeze
after its first use to ensure its immutable in your init scenario.
const myInitObject = {}
export default myInitObject
then in your init method referencing it:
import myInitObject from './myInitObject'
myInitObject.someProp = 'i am about to get cold'
Object.freeze(myInitObject)
The myInitObject
will still be global as it can be referenced anywhere as an import but will remain frozen and throw if anyone attempts to modify it.
Example of react state using singleton
https://codesandbox.io/s/adoring-architecture-ru3vt (see UserContext.tsx)
If using react-create-app
(what I was looking for actually) In this scenario you can also initialize global objects cleanly when referencing environment variables.
Creating a .env file at the root of your project with prefixed REACT_APP_
variables inside does quite nicely. You can reference within your JS and JSX process.env.REACT_APP_SOME_VAR
as you need AND it's immutable by design.
This avoids having to set window.myVar = %REACT_APP_MY_VAR%
in HTML.
See more useful details about this from Facebook directly:
https://facebook.github.io/create-react-app/docs/adding-custom-environment-variables
Solution 2 - Reactjs
Why don't you try using Context?
You can declare a global context variable in any of the parent components and this variable will be accessible across the component tree by this.context.varname
. You only have to specify childContextTypes
and getChildContext
in the parent component and thereafter you can use/modify this from any component by just specifying contextTypes
in the child component.
However, please take a note of this as mentioned in docs:
> Just as global variables are best avoided when writing clear code, you should avoid using context in most cases. In particular, think twice before using it to "save typing" and using it instead of passing explicit props.
Solution 3 - Reactjs
Is not recommended but.... you can use componentWillMount from your app class to add your global variables trough it... a bit like so:
componentWillMount: function () {
window.MyVars = {
ajax: require('../helpers/ajax.jsx'),
utils: require('../helpers/utils.jsx')
};
}
still consider this a hack... but it will get your job done
btw componentWillMount executes once before rendering, see more here: https://reactjs.org/docs/react-component.html#mounting-componentwillmount
Solution 4 - Reactjs
Create a file named "config.js" in ./src folder with this content:
module.exports = global.config = {
i18n: {
welcome: {
en: "Welcome",
fa: "خوش آمدید"
}
// rest of your translation object
}
// other global config variables you wish
};
In your main file "index.js" put this line:
import './config';
Everywhere you need your object use this:
global.config.i18n.welcome.en
Solution 5 - Reactjs
Can keep global variables in webpack i.e. in webpack.config.js
externals: {
'config': JSON.stringify({ GLOBAL_VARIABLE: "global var value" })
}
In js module can read like
var config = require('config')
var GLOBAL_VARIABLE = config.GLOBAL_VARIABLE
Hope this will help.
Solution 6 - Reactjs
Here is a modern approach, using globalThis
, we took for our React Native app.
globalThis
is now included in...
- Modern browsers - MDN documentation
- Typescript 3.4 - Handbook documentation
- ESLint v7 - Release notes
appGlobals.ts
// define our parent property accessible via globalThis. Also apply the TypeScript type.
var app: globalAppVariables;
// define the child properties and their types.
type globalAppVariables = {
messageLimit: number;
// more can go here.
};
// set the values.
globalThis.app = {
messageLimit: 10,
// more can go here.
};
// Freeze so these can only be defined in this file.
Object.freeze(globalThis.app);
App.tsx (our main entry point file)
import './appGlobals'
// other code
anyWhereElseInTheApp.tsx
const chatGroupQuery = useQuery(GET_CHAT_GROUP_WITH_MESSAGES_BY_ID, {
variables: {
chatGroupId,
currentUserId: me.id,
messageLimit: globalThis.app.messageLimit, // 👈 used here.
},
});
Solution 7 - Reactjs
The best way I have found so far is to use React Context but to isolate it inside a high order provider component.
Solution 8 - Reactjs
Maybe it's using a sledge-hammer to crack a nut, but using environment variables (with Dotenv https://www.npmjs.com/package/dotenv) you can also provide values throughout your React app. And that without any overhead code where they are used.
I came here because I found that some of the variables defined in my env files where static throughout the different envs, so I searched for a way to move them out of the env files. But honestly I don't like any of the alternatives I found here. I don't want to set up and use a context everytime I need those values.
I am not experienced when it comes to environments, so please, if there is a downside to this approach, let me know.
Solution 9 - Reactjs
For only declaring something, try this. Make sure MyObj
is assigned at the proper time for you want to access it in render()
, many ways was published before this thread. Maybe one of the simplest ways if undefined then create it
does the job.
declare global {
interface Window {
MyObj: any;
}
}
Solution 10 - Reactjs
Create a file :
import React from "react";
const AppContext = {};
export default AppContext;
then in App.js, update the value
import AppContext from './AppContext';
AppContext.username = uname.value;
Now if you want the username to be used in another screen:
import AppContext from './AppContext';
AppContext.username to be used for accessing it.
Solution 11 - Reactjs
GlobalThis may be supported in some browsers.
You can refer following links
https://webpack.js.org/plugins/provide-plugin/
https://webpack.js.org/plugins/define-plugin/
Solution 12 - Reactjs
I don't know what they're trying to say with this "React Context" stuff - they're talking Greek, to me, but here's how I did it:
Carrying values between functions, on the same page
In your constructor, bind your setter:
this.setSomeVariable = this.setSomeVariable.bind(this);
Then declare a function just below your constructor:
setSomeVariable(propertyTextToAdd) {
this.setState({
myProperty: propertyTextToAdd
});
}
When you want to set it, call this.setSomeVariable("some value");
(You might even be able to get away with this.state.myProperty = "some value";
)
When you want to get it, call var myProp = this.state.myProperty;
Using alert(myProp);
should give you some value
.
Extra scaffolding method to carry values across pages/components
You can assign a model to this
(technically this.stores
), so you can then reference it with this.state
:
import Reflux from 'reflux'
import Actions from '~/actions/actions'
class YourForm extends Reflux.Store
{
constructor()
{
super();
this.state = {
someGlobalVariable: '',
};
this.listenables = Actions;
this.baseState = {
someGlobalVariable: '',
};
}
onUpdateFields(name, value) {
this.setState({
[name]: value,
});
}
onResetFields() {
this.setState({
someGlobalVariable: '',
});
}
}
const reqformdata = new YourForm
export default reqformdata
Save this to a folder called stores
as yourForm.jsx
.
Then you can do this in another page:
import React from 'react'
import Reflux from 'reflux'
import {Form} from 'reactstrap'
import YourForm from '~/stores/yourForm.jsx'
Reflux.defineReact(React)
class SomePage extends Reflux.Component {
constructor(props) {
super(props);
this.state = {
someLocalVariable: '',
}
this.stores = [
YourForm,
]
}
render() {
const myVar = this.state.someGlobalVariable;
return (
<Form>
<div>{myVar}</div>
</Form>
)
}
}
export default SomePage
If you had set this.state.someGlobalVariable
in another component using a function like:
setSomeVariable(propertyTextToAdd) {
this.setState({
myGlobalVariable: propertyTextToAdd
});
}
that you bind in the constructor with:
this.setSomeVariable = this.setSomeVariable.bind(this);
the value in propertyTextToAdd
would be displayed in SomePage
using the code shown above.