I am trying to convert this class component to functional component using hooks
import React, { Component, cloneElement } from 'react';
class Dialog extends Component {
constructor(props) {
super(props);
this.id = uuid();
}
render(){
return ( <div>Hello Dialog</div> );
}
}
This component is initiated with a specific ID because I may have to use multiple instances of them. How can I achieve this if I use functional component?
One solution would be to use useEffect to create your ID at the first render, and store it in the state :
const Dialog = () => {
const [id, setId] = useState(null);
useEffect(() => {
setId(uuid())
}, [])
return <div>Hello Dialog</div>
}
Giving an empty array as the second parameter of useEffect makes it unable to trigger more than once.
But another extremely simple solution could be to just... create it outside of your component :
const id = uuid();
const Dialog = () => {
return <div>Hello Dialog</div>
}
You may store it in state:
const [id] = useState(uuid()); // uuid will be called in every render but only the first one will be used for initiation
// or using lazy initial state
const [id] = useState(() => uuid()); // uuid will only be called once for initiation
You may also store it in React ref:
const id = useRef(null);
if(!id.current) {
// initialise
id.current = uuid();
}
// To access it’s value
console.log(id.current);
Any instance property becomes a ref pretty much, and you would access idRef.current in this case for the id
function Dialog() {
const idRef = useRef(uuid())
return <div>Hello Dialog</div>
}
Thank you all, your solutions works well. I also try this solution and I find it OK too: replace this.id with Dialog.id. Is there any downside with this solution?
Related
I am using the useIsDirty hook in two components, CustomCodeEditor and EditorFooter, to track whether the code in the Editor has been modified. The hook returns an isDirty state and a setIsDirty function to update it. When I call setIsDirty(true) in the CustomCodeEditor component, the state is updated, but when I call setIsDirty(false) in the EditorFooter component, it doesn't seem to update the isDirty state. I believe this is because the EditorFooter component does not have access to the updated state. Anyone, please help me with this.
useIsDirty:
import { useEffect, useState } from "react"
const useIsDirty = () => {
const [isDirty, setIsDirty] = useState(false)
useEffect(() => {
const handleBeforeUnload = (event) => {
if (isDirty) {
event.preventDefault()
event.returnValue = ""
alert("You have unsaved changes, are you sure you want to leave?")
}
}
console.log("Diryt:", isDirty)
window.addEventListener("beforeunload", handleBeforeUnload)
return () => {
window.removeEventListener("beforeunload", handleBeforeUnload)
}
}, [isDirty])
return { isDirty, setIsDirty }
}
export default useIsDirty
CustomCodeEditor
import Editor from "#monaco-editor/react"
import useIsDirty from "../../hooks/useIsDirty"
const CustomCodeEditor = () => {
const { isDirty, setIsDirty } = useIsDirty()
console.log("isDirty:", isDirty)
return (
<div className="bg-[#1e1e1e] h-full">
<Editor
onChange={(value) => {
updateCode(value || "")
setIsDirty(true) // updating state
}}
/>
</div>
)
}
export default CustomCodeEditor
EditorFooter
import Button from "../reusable/Button"
const EditorFooter = () => {
const { setIsDirty } = useIsDirty()
const handleSave = async () => {
setIsDirty(false)
}
return (
<div>
<Button
onClick={handleSave}
>
Save
</Button>
<Button
onClick={handleSave}
>
Submit
</Button>
</div>
)
}
export default EditorFooter
Hooks are not singleton instances.. when you use useIsDirty somewhere.. it always create new instance, with unrelated states to other ones. If you want to share this state you need to use Context
const IsDirtyContext = createContext(undefined);
const IsDirtyProvider = ({ children }): ReactElement => {
const [isDirty, setIsDirty] = useState(false)
return <IsDirtyContext.Provider value={{isDirty, setIsDirty}}>{children}</IsDirtyContext.Provider>;
};
and then you should wrap your commponent tree where you wanna access it with IsDirtyProvider
after that, you can even create your custom hook that will just return that context:
const useIsDirty = () => {
return useContext(IsDirtyContext)
}
Looking at your question, it looks like you are trying to use the same state in both components. However, the state doesn't work like that. A new instance is created whenever you make a call to useIsDirty from a different component.
If you want to use the state value across two components. You can do that using one of the following ways.
1 - Use a parent and child hierarchy.
Steps
Create a parent component and wrap the two components inside the parent component.
Manage the state in the parent component and pass it using props to the child component.
Create a function in child components that will execute a function from the parent component. The parent component function will hold the code to update the state based on whatever value you receive from the child component.
Now you should be able to share your state between both components.
2 - Use the context api.
If you are not familiar with what context api is, below is a brief explanation.
Context api helps you share data between components, without the need of passing them as a prop to each and every component.
You can use createContext and useContext hooks from context api.
createContext is used to create a new context provider.
useContext hook is used to manage the state globally.
You can get the value from context using this function.
Whenever the state is updated the value will be reflected globally.
Note - Any component that needs to use the value inside the useContext should be wrapped inside the useContext provider component.
Steps to create a context provider.
To create a context you just need to use the react hook createContext
Create a context using below code
const isDirtyContext = createContext();
Wrap your components in the context provider
import {IsDirtyContext} from './path/filename'
<IsDirtyContext.Provider value={[isDirty, setIsDirty]}>{children}</IsDirtyContext.Provider>
If your context is in a separate file, then you can import it into any child component using the import statement.
import {IsDirtyContext} from './path/filename'
Use the context
const [isDirty] = useContext(IsDirtyContext);
Now the isDirty state value is available globally in all components.
Hope this information helps you. Please upvote if this helps you understand and solve the problem.
I have a hoc component like this:
export const withAttrs = (WrappedComponent) => {
const ModifiedComponent = (props) => (
<WrappedComponent {...props} data-test-id="this-is-a-element" />
);
return ModifiedComponent;
};
export default withAttrs;
and I use it like this:
import React from 'react';
import withAttrs from './withAttrs';
const SomeLink = () => <a><p>hey</p</a>;
export default withAttrs(SomeLink);
I expect to have an anchor tag like this:
<a data-test-id="this-is-a-element"><p>hey</p></a>
But the hoc doesn't add the data-attribute to the first element. Is there a way to achieve this?
But the hoc doesn't add the data-attribute to the first element.
It's not the HOC that isn't adding it, it's SomeLink, which doesn't do anything with the props the HOC passes to it.
The simple answer is to update SomeLink:
const SomeLink = (props) => <a {...props}><p>hey</p></a>;
That's by far the better thing to do than the following.
If you can't do that, you could make your HOC add the property after the fact, but it seems inappropriate to have the HOC reach inside the component and change things. In fact, React makes the element objects it creates immutable, which strongly suggests you shouldn't try to mess with them.
Still, it's possible, it's probably just a bad idea:
export const withAttrs = (WrappedComponent) => {
const ModifiedComponent = (props) => {
// Note we're *calling* the function, not just putting it in
// a React element via JSX; we're using it as a subroutine of
// this component rather than as its own component.
// This will only work with function components. (You could
// write a version that handles class components as well,
// but offhand I don't think you can make one HOC that handles
// both in this case.)
const result = WrappedComponent(props);
return {
...result,
props: {
...result.props,
"data-test-id": "this-is-a-element",
},
};
};
return ModifiedComponent;
};
/*export*/ const withAttrs = (WrappedComponent) => {
const ModifiedComponent = (props) => {
// Note we're *calling* the function, not just putting it in
// a React element via JSX; we're using it as a subroutine of
// this component rather than as its own component.
// This will only work with function components. (You could
// write a version that handles class components as well,
// but offhand I don't think you can make one HOC that handles
// both in this case.)
const result = WrappedComponent(props);
// THIS IS PROBABLY A VERY BAD IDEA. React makes these objects
// immutable, probably for a reason. We shouldn't be mucking
// with them.
return {
...result,
props: {
...result.props,
"data-test-id": "this-is-a-element",
},
};
};
return ModifiedComponent;
};
const SomeLink = () => <a><p>hey</p></a>;
const SomeLinkWrapped = withAttrs(SomeLink);
const Example = () => {
return <div>
<div>Unwrapped:</div>
<SomeLink />
<div>Wrapped:</div>
<SomeLinkWrapped />
</div>;
};
const root = ReactDOM.createRoot(document.getElementById("root"));
root.render(<Example />);
/* So we can see that it was applied */
[data-test-id=this-is-a-element] {
color: green;
}
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/18.1.0/umd/react.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/18.1.0/umd/react-dom.development.js"></script>
Again, I don't think I'd do that except as a very last resort, and I wouldn't be surprised if it breaks in future versions of React.
I need to have a component for handling settings, this component (called Settings) stores state using useState(), for example the primary color.
I need to create a single instance of this component and make it available to every component in the app. Luckily, I already pass down a state dict to every component (I'm very unsure if this is the correct way to achieve that btw), so I can just include this Settings constant.
My problem is that I don't know how to create the component for this purpose, so that I can call its functions and pass it to children.
Here is roughly what my Settings component looks like:
const Settings = (props) => {
const [primaryColor, setPrimaryColor] = useState("")
const getColorTheme = (): string => {
return primaryColor
}
const setColorTheme = (color: string): void => {
setPrimaryColor(color)
}
return null
}
export default Settings
Then I would like to be able to do something like this somewhere else in the app:
const App = () => {
const settings = <Settings />
return (
<div style={{ color: settings.getColorTheme() }}></div>
)
}
Bear in mind that I'm completely new to react, so my approach is probably completely wrong.
You can use a custom Higher Order Component(HOC) for this purpose, which is easier than creating a context(even thougn context is also a HOC). A HOC takes a component and returns a new component. You can send any data from your HOC to the received component.
const withSettings = (Component) => {
const [settings, setSettings] = useState({})
// ...
// ...
<Component {...props} settings={settings}/>
);
And you can use it like this:
const Component = ({ settings }) => {
...your settings UI
}
export default SettingsUI = withSettings(Component);
You can read more about HOCs in the official react documentation
I want to have a global object that is available to my app where I can retrieve the value anywhere and also set a new value anywhere. Currently I have only used Context for values that are related to state i.e something needs to render again when the value changes. For example:
import React from 'react';
const TokenContext = React.createContext({
token: null,
setToken: () => {}
});
export default TokenContext;
import React, { useState } from 'react';
import './App.css';
import Title from './Title';
import TokenContext from './TokenContext';
function App() {
const [token, setToken] = useState(null);
return(
<TokenContext.Provider value={{ token, setToken }}>
<Title />
</TokenContext.Provider>
);
}
export default App;
How would I approach this if I just want to store a JS object in context (not a state) and also change the value anywhere?
The global context concept in React world was born to resolve problem with passing down props via multiple component layer. And when working with React, we want to re-render whenever "data source" changes. One way data binding in React makes this flow easier to code, debug and maintain as well.
So what is your specific purpose of store a global object and for nothing happen when that object got changes? If nothing re-render whenever it changes, so what is the main use of it?
Prevent re-render in React has multiple ways like useEffect or old shouldComponentUpdate method. I think they can help if your main idea is just prevent re-render in some very specific cases.
Use it as state management libraries like Redux.
You have a global object (store) and you query the value through context, but you also need to add forceUpdate() because mutating the object won't trigger a render as its not part of React API:
const globalObject = { counter: 0 };
const Context = React.createContext(globalObject);
const Consumer = () => {
const [, render] = useReducer(p => !p, false);
const store = useContext(Context);
const onClick = () => {
store.counter = store.counter + 1;
render();
};
return (
<>
<button onClick={onClick}>Render</button>
<div>{globalObject.counter}</div>
</>
);
};
const App = () => {
return (
<Context.Provider value={globalObject}>
<Consumer />
</Context.Provider>
);
};
I am trying to change a class when onClick event is fired, my function is called and it seems to be working but the class just won't update un the render, this is my code:
import React from 'react';
const Something = props => {
let opened = false;
const toggle = () => {
opened = !opened;
};
return (
<div className={opened ? 'some-class opened' : 'some-class'}>
<div className="some-inner-class" onClick={toggle}>
...content
</div>
</div>
);
};
export default Something;
I just want to be able to change style on when click event is fired.
My suggestion to you will be to use react hooks in this scenario, by that I mean, something like this, I have updated your code with my suggestion;
Hope it helps;
import React, { useState } from 'react';
const Something = props => {
// ***because this doesn't exist in a function component and we'd want to persist this value of opened between function call, a react hook in a function component will be ideal in your case.
//let opened = false;
// *suggestion as per react documentation: useState hook lets us keep local state in a function component
const [opened, setOpened] = useState(false);
// ***you don't really need this part, see my approach in second div of return
// const toggle = () => {
// opened = !opened;
// };
return (
<div className={opened ? 'some-class opened' : 'some-class'}>
<div className="some-inner-class" onClick={() => setOpened(true)}>
<p>Click me</p>
</div>
</div>
);
};
export default Something;
You need to update state in React for a rerender to occur. You should be creating state in a constructor like:
constructor() {
super();
this.state = { toggled: false };
}
Then, in your toggle function you need to call
this.setState({toggled: !this.state.toggled});
Currently your component is a stateless functional component so you would either need to rewrite it as a class that extends React.component or you could use hooks, https://reactjs.org/docs/hooks-state.html. Since it looks like you're just starting to learn how to use React I would rewrite the component as a class first and then try to refactor it using hooks (the modern practice).