I'm creating a react app with useState and useContext for state management. So far this worked like a charm, but now I've come across a feature that needs something like an event:
Let's say there is a ContentPage which renders a lot of content pieces. The user can scroll through this and read the content.
And there's also a BookmarkPage. Clicking on a bookmark opens the ContentPage and scrolls to the corresponding piece of content.
This scrolling to content is a one-time action. Ideally, I would like to have an event listener in my ContentPage that consumes ScrollTo(item) events. But react pretty much prevents all use of events. DOM events can't be caught in the virtual dom and it's not possible to create custom synthetic events.
Also, the command "open up content piece XYZ" can come from many parts in the component tree (the example doesn't completely fit what I'm trying to implement). An event that just bubbles up the tree wouldn't solve the problem.
So I guess the react way is to somehow represent this event with the app state?
I have a workaround solution but it's hacky and has a problem (which is why I'm posting this question):
export interface MessageQueue{
messages: number[],
push:(num: number)=>void,
pop:()=>number
}
const defaultMessageQueue{
messages:[],
push: (num:number) => {throw new Error("don't use default");},
pop: () => {throw new Error("don't use default");}
}
export const MessageQueueContext = React.createContext<MessageQueue>(defaultMessageQueue);
In the component I'm providing this with:
const [messages, setmessages] = useState<number[]>([]);
//...
<MessageQueueContext.Provider value={{
messages: messages,
push:(num:number)=>{
setmessages([...messages, num]);
},
pop:()=>{
if(messages.length==0)return;
const message = messages[-1];
setmessages([...messages.slice(0, -1)]);
return message;
}
}}>
Now any component that needs to send or receive messages can use the Context.
Pushing a message works as expected. The Context changes and all components that use it re-render.
But popping a message also changes the context and also causes a re-render. This second re-render is wasted since there is no reason to do it.
Is there a clean way to implement actions/messages/events in a codebase that does state management with useState and useContext?
Since you're using routing in Ionic's router (React-Router), and you navigate between two pages, you can use the URL to pass params to the page:
Define the route to have an optional path param. Something like content-page/:section?
In the ContentPage, get the param (section) using React Router's useParams. Create a useEffect with section as the only changing dependency only. On first render (or if section changes) the scroll code would be called.
const { section } = useParams();
useEffect(() => {
// the code to jump to the section
}, [section]);
I am not sure why can't you use document.dispatchEvent(new CustomEvent()) with an associated eventListener.
Also if it's a matter of scrolling you can scrollIntoView using refs
Related
In my react app I use the following pattern quite a bit:
export default function Profile() {
const [username, setUsername] = React.useState<string | null>(null);
React.useEffect(()=>{
fetch(`/api/userprofiles?username=myuser`)
.then(res=>res.json())
.then(data => setUsername(data.username))
},[])
return(
<div>
{username}'s profile
</div>
)
}
When the page loads, some user data is fetched from the server, and then the page updates with that user data.
One thing I notice is that I only really need to call setUsername() once on load, which makes using state seem kinda excessive. I can't shake the feeling that there must be a better way to do this in react, but I couldn't really find an alternative when googling. Is there a more efficient way to do this without using state? Or is this the generally agreed upon way to load data when it only needs to be done once on page load
Without using any external libraries, no - that is the way to do it.
It would be possible to remove the state in Profile and have it render the username from a prop, but that would require adding the state into the parent component and making the asynchronous request there. State will be needed somewhere in the app pertaining to this data.
The logic can be abstracted behind a custom hook. For example, one library has useFetch where you could do
export default function Profile() {
const { data, error } = useFetch('/api/userprofiles?username=myuser');
// you can check for errors if desired...
return(
<div>
{data.username}'s profile
</div>
)
}
Now the state is inside useFetch instead of in your components, but it's still there.
To give a bit of context, I am conducting a research focused on digital marketing and user experience. To enable the research, it is essential that I am able to get event logs from every component in an UI so I am, then, able to create datasets of usability pattern.
To do so in a web interface, e.g. using JavaScript, that's very simple.
window.addEventListener("someEvent", (e) => {//do something with the data});
The e element gives me everything I need, and If I want to listen to all window events, I can run a for loop through the window object events and add an event listener to each. My issue is with mobile development. For cross application reasons, am I am using React Native to try to create the same effect as window.addEventListener to mobile apps.
This is my first time using React Native. After a bit of searching, I am now aware that React Native does not have a window object (at least not as we understand window in JavaScript) and that the interface is translated to the platform native components, so document.getElementBy... would't work either.
What I though of was refs. I would only need to add a reference to the top component App. So what I have working so far:
export default function App() {
const viewRef = useRef();
useEffect(() => {
//I can use ref here to iterate through all events of View and
//bind event listeners to it
}, [viewRef]);
return (
<View
ref={viewRef}
style={styles.container}
onTouchEnd={(e) => {
console.log(e.target);
}}
>
<DummyComponent />
</View>
);
}
onTouchEnd event is bind to the top-layer component, so I can get everything that is a child of it. In that useEffect, I can do the same thing I would with JavaScript's window.
So I guess this is one way to do it. However, in my research I would like to enable any React Native app to begin logging events seamlessly. The state of the art would be creating a dependency that would being logging everything simply by installing it. That said, how can I iterate a React Native application to find Views and bind their events, without need to add ANYTHING to the actual component?
In JavaScript it would be something like:
document.getElementsByTagName("View").map((view) => {//bind view events});
So I'm not sure if this can help, but you can change the defaultProps of a component on start of your application.
So using your code as example you could do something like this:
const listener = e => {
console.log(e);
}
View.defaultProps = {
...View.defaultProps, // maintains original default props
onTouchEnd: listener
};
Basically this way you can have a global listener for each View component
I have a very large and complex React application. It is designed to behave like a desktop application. The interface is a document style interface with tabs, each tab can be one of many different type of editor component (there are currently 14 different editor screens). It is possible to have a very large number of tabs open at once (20-30 tabs). The application was originally written all with React class components, but with newer components (and where significant refactors have been required) I've moved to functional components using hooks. I prefer the concise syntax of functions and that seems to be the recommended direction to take in general, but I've encountered a pattern from the classes that I don't know how to replicate with functions.
Basically, each screen (tab) on the app is an editor of some sort (think Microsoft office, but where you can have a spreadsheet, text document, vector image, Visio diagram, etc all in tabs within the same application... Because each screen is so distinct they manage their own internal state. I don't think Redux or anything like that is a good solution here because the amount of individually owned bits of state are so complex. Each screen needs to be able to save it's current working document to the database, and typically provides a save option. Following standard object oriented design the 'save' function is implemented as a method on the top level component for each editor. However I need to perform a 'save-all' function where I iterate through all of the open tabs and call the save method (using a reference) on each of the tabs. Something like:
openTabs.forEach((tabRef) => tabRef.current.save());
So, If I make this a functional component then I have my save method as a function assigned to a constant inside the function:
const save = () => {...}
But how can I call that from a parent? I think the save for each component should live within that component, not at a higher level. Aside from the fact that would make it very difficult to find and maintain, it also would break my modular loading which only loads the component when needed as the save would have to be at a level above the code-splitting.
The only solution to this problem that I can think of is to have a save prop on the component and a useEffect() to call the save when that save prop is changed - then I'd just need to write a dummy value of anything to that save prop to trigger a save... This seems like a very counter-intuitive and overly complex way to do it.... Or do I simply continue to stick with classes for these components?
Thankyou,
Troy
But how can I call that from a parent? I think the save for each component should live within that component, not at a higher level.
You should ask yourself if the component should be smart vs dumb (https://www.digitalocean.com/community/tutorials/react-smart-dumb-components).
Consider the following:
const Page1 = ({ onSave }) => (...);
const Page2 = ({ onSave }) => (...);
const App = () => {
const handleSavePage1 = (...) => { ... };
const handleSavePage2 = (...) => { ... };
const handleSaveAll = (...) => {
handleSavePage1();
handleSavePage2();
};
return (
<Page1 onSave={handleSavePage1} />
<Page2 onSave={handleSavePage2} />
<Button onClick={handleSaveAll}>Save all</button>
);
};
You've then separated the layout from the functionality, and can compose the application as needed.
I don't think Redux or anything like that is a good solution here because the amount of individually owned bits of state are so complex.
I don't know if for some reason Redux is totally out of the picture or not, but I think it's one of the best options in a project like this.
Where you have a separated reducer for each module, managing the module's state, also each reducer having a "saveTabX" action, all of them available to be dispatched in the Root component.
I have a static website made with react that requests data from the backend in the useEffect() hook:
export default const App = () => {
const [data, setData] = useState("");
useEffect(() => {
server.get().then(data => {
setData(data)
})
})
return(
<title>{data}</title>
<h1>{data}</h1>
)
}
However, when Bing crawls the webpage, the following problem occurs:
Bing Screenshot:
<title></title>
<h1></h1>
How can I solve this issue?
React isn't used for static sites. If you'd like to have better SEO and server-side rendering you can use nextjs.
The way your app is setup currently will only return some HTML with and empty body to a GET request to / (which is what I suppose crawlers like the one you mentioned use) and starts rendering components after the JavaScript is loaded.
But if you decide on a server-side rendering approach, whenever a request is made to your app the server will first render the app on it's side and the return an HTML string with the rendered components.
Did you check if your server.get() is returning some data? I can't see any url here, so maybe it's actually returning nothing.
Even so, maybe you forgot to pass the second argument of useEffect, which is an array of arguments, which this hooks uses to trigger itself. For example, if you want to trigger only once, when component is mounted, you need to pass [] as second argument of useEffect.
I have a component, lets call component 1. A method in component1 makes an axios.post request and the server returns a bunch of data. When data is loaded, a new button appears. When this button is clicked, it will be navigated to another route with another component, let call this component2. Now some of the loaded data from component1 needs to transferred to component2 and should be opened in new tab. Below is the code:
<script>
import axios from 'axios';
export default {
name: "CheckStandard",
data() {
return {
standard: '',
time: {},
programs: {},
example: {},
}
},
methods: {
checkData(){
let std= {
std: this.standard,
}
axios.post('http://localhost:3000/postdata', std)
.then(res => {
if (res.status === 200) {
if (res.data === 0) {
this.invalidID = "This Standard does not exist"
}
else {
let data = res.data
this.time = res.data["Starttime"];
this.programs = res.data["program"]
this.example = res.data["example"]
}
}).catch(error => {
console.log(error);
this.error = error.response
})
},
}
goToPictures(){
let route = this.$router.resolve({
name:'ProgramCheckList',
params: {
programs: this.programs,
time: this.time,
example: this.example
}
})
window.open(route.href,'_blank')
},
}
}
</script>
The function goToPictures is the function that is invoked after clicking the button. Now in this function goToPictures I have defined the route to navigate to another tab. But the problem the data in the params which it should carry is lost. I tried with $router.push ofcourse it works but it is not to open in new tab. Below is the code for the same:
goToPictures(){
this.$router.resolve({
name:'ProgramCheckList',
params: {
programs: this.programs,
time: this.time,
example: this.example
}
})
},
}
Since I am new to vue, I have tried my best to look for an answer for this, even I have came across some posts in several forums mentioning, it is may be not be possible even, instead advised to use vuex. But I still wanted to post it, maybe we have a solution now or any other idea. Thanks
The problem you're seeing stems from the fact that, when you open a new window, Vue is basically going to re-render your components as if you hit refresh. Your Component 2 has props that it can only inherit from another component, and as such, it has no possible way of knowing what the props it needs to use are.
To illustrate in simple terms what's happening:
The user navigates to Component 1. They click the button, which makes the GET request. You now have some data that you can pass onto Component 2 as props.
In a regular environment, the user would simply click on the link leading to Component 2, and the props would be passed on normally, and everything would work as intended.
The problem in your situation is that Component 2 depends on Component 1 for its data. By navigating directly to the Component 2 route (in this situation, opening a new window is functionally identical to a user copy/pasting the url into the adress bar), Vue never has the chance of interacting with Component 1, and never gets told where to get the props it needs to populate Component 2.
Overcoming the issue
There's a few things you can do here to overcome this issue. The most obvious one is to simply open Component 2 as you would normally, without opening a new window, but keep in mind that even if you do this, should a user copy/paste the URL where Component 2 is, they'll run into the exact same issue.
To properly deal with the issue, you have to specify a way for Component 2 to grab the data it needs. Since the data is already fetched, it makes sense to do this in the created() or mounted() hooks, though if you wanted to you could also deal with this in Vue Router's beforeRouteEnter() hook.
Vuex
While you don't necessarily need a state management tool like Vuex, it's probably the simplest way for your needs. When you grab the data from Component 1, store it and access it from the Component 2 mounted() hook. Easy-peasy.
localStorage()
Alternatively, depending on how the data is being served, you could use localStorage(). Since you're opening a new window, sessionStorage() won't work. Do note that localStorage() can only hold strings and nothing else, and isn't necessarily available in every browser.
You can store the data to a global variable and use that in the newly opened window. Asked here Can I pass a JavaScript variable to another browser window?
Provided the windows are from the same security domain, and you have a reference to the other window, yes.
Javascript's open() method returns a reference to the window created (or existing window if it reuses an existing one). Each window created in such a way gets a property applied to it "window.opener" pointing to the window which created it.
Either can then use the DOM (security depending) to access properties of the other one, or its documents,frames etc.
Another example from same thread:
var thisIsAnObject = {foo:'bar'};
var w = window.open("http://example.com");
w.myVariable = thisIsAnObject;
//or this from the new window
var myVariable = window.opener.thisIsAnObject;