Should Javascript ES6 Classes be Used as React State? - javascript

Should ES6 classes be used directly as React state?
I want to define an ES6 class that:
Has member variables that will be displayed on the frontend. (changes to them trigger re-renders)
Has methods that sync those member variables with my backend periodically as they change.
However, calling setState does not appear to diff class members, at least as far as I can tell.
Using the following class:
class Document{
constructor(){
this.title = "";
this.body = "";
}
syncWithDatabase = async () => {
// do some logic to update the database
}
}
And this component:
// import Document from "...";
export default function Sandbox() {
const [document, setDocument] = useState(new Document());
const [renderTrigger, setRenderTrigger] = useState(false);
return (
<div>
<div>{document.title}</div>
<div>{document.body}</div>
<button
onClick={() => {
document.title = 'Some Default Title';
document.body = 'lorem text';
document.syncWithDatabase(); // being able to take this type of action in this way is why I'm trying to use classes.
setDocument(document);
}}
>
Set Canned Data
</button>
<div>Render trigger is: {renderTrigger ? 'true' : 'false'}</div>
<button onClick={() => setRenderTrigger(true)}>Force Render</button>
</div>
);
}
Clicking the first button will set the title and body on the instance of Document held react state, but it will not update the UI.
Clicking the second button to force a re-render in a way that I am confident will work makes the updated members of document render out, even though they didn't when setDocument is called.
Creating a new object with new Document() and passing it setDocument WILL trigger a re-render. So I'm thinking that react isn't doing a deep compare or is seeing that the reference to the Document object has not changed, and therefore not re-rending.
So, is it possible to change an object's members, pass that object to a setState hook and have it update the UI, without creating an entirely new object? Or should I avoid doing what I'm trying to do here?

You can (but probably shouldn't, see below) use an object created by a constructor function (which is what document is in your code) as state. What you can't do is directly modify it as you are here (see the documentation):
document.title = 'Some Default Title'; // <=== INCORRECT
document.body = 'lorem text'; // <=== INCORRECT
document.syncWithDatabase();
setDocument(document); // <=== INCORRECT
Instead, you'd need to create a new document object
const newDoc = new Document();
newDoc.title = 'Some Default Title';
newDoc.body = 'lorem text';
newDoc.syncWithDatabase();
setDocument(newDoc);
That said, when using the useState hook, you're usually better off keeping your state variables discrete (having one for title and one for body), so that changing one doesn't require also changing the other (unless, of course, they always change together). The documentation discusses that here; here's one quote:
...we recommend to split state into multiple state variables based on which values tend to change together.
(their emphasis)

Related

Reactivity on props Vue.js

I am in the beginning of learning Vue, and having a hard time understanding how to define props etc. using the composition API.
I have a component (ACE Editor), loaded like this:
<v-ace-editor
v-model:value="currentRecord.text"
/>
The v-ace-editor needs to have the model and value loaded like this: v-model:value.
import {computed, ref} from 'vue';
import collect from "collect.js"
const props = defineProps({
records: {
type: Object,
},
})
//Get all records.
let getRecords = () => {
return collect(props.records)
}
//Filter the records using "collect.js"
const getUnlabeledRecords = () => {
return getRecords()
.where('skipped', false)
.where('processed', false);
}
//Assign all unlabeled records on the first load.
let allRecords = ref(getUnlabeledRecords());
//In order to check if "text" is empty - and if not, set a default value, load the first record into a temp. variable.
let first = allRecords.value.first();
if(first){
first.text ??= "";
}
//Load the current record into a ref.
let current = ref(first);
//Finally, compute it.
let currentRecord = computed(() => current.value)
Looking at this, and coming from a backend background, it feels very bloated.
I have tried the following:
let allRecords = ref(getUnlabeledRecords());
let currentRecord = computed(() => allRecords.value.first())
But doing this leads to me not being able to interact with the currentRecord - nor change the allRecords. This means that if for example currentRecord.text is null from the backend, my ace-editor component fails because it expects a value.
Is there another way to load in these variables?
You actually don't have to called .value of a ref when using it in the template.
So you can actually remove the computed part (last line of your ) and change your template to.
<v-ace-editor
v-model="current.text"
/>
Now, assuming you managed v-model correctly in v-ace-editor (if this is your own component), you should have reactivity kept when modifiying current.text from v-ace-editor.
As a side note, computed properties are read-only. You cannot expect a child component to modify its value by passing it with v-model.
However, you should note that updating records prop from parent component will not update current. For this, maybe you want to add a watcher on records.
Also, personal suggestion, but if you only really care about currentRecord in your component and not all records, maybe you should do the filtering from parent component and only pass currentRecord as a prop. Other personal suggestion, you can declare all your variables in your script with const instead of let. const prevent reassignation, but since you work with refs, you never reassign it, but you change its value property.

Vue child component not displaying dynamic data on first page load

Given the code below, my child component alerts trigger before any of the code in the Parent mounted function.
As a result it appears the child has already finished initialization before the data is ready and therefor won't display the data until it is reloaded.
The data itself comes back fine from the API as the raw JSON displays inside the v-card in the layout.
My question is how can I make sure the data requested in the Parent is ready BEFORE the child component loads? Anything I have found focuses on static data passed in using props, but it seems this completely fails when the data must be fetched first.
Inside the mounted() of the Parent I have this code which is retrieves the data.
const promisesArray = [this.loadPrivate(),this.loadPublic()]
await Promise.all(promisesArray).then(() => {
console.log('DATA ...') // fires after the log in Notes component
this.checkAttendanceForPreviousTwoWeeks().then(()=>{
this.getCurrentParticipants().then((results) => {
this.currentP = results
this.notesArr = this.notes // see getter below
})
The getter that retrieves the data in the parent
get notes() {
const newNotes = eventsModule.getNotes
return newNotes
}
My component in the parent template:
<v-card light elevation="">
{{ notes }} // Raw JSON displays correctly here
// Passing the dynamic data to the component via prop
<Notes v-if="notes.length" :notesArr="notes"/>
</v-card>
The Child component:
...
// Pickingn up prop passed to child
#Prop({ type: Array, required: true })
notesArr!: object[]
constructor()
{
super();
alert(`Notes : ${this.notesArr}`) // nothing here
this.getNotes(this.notesArr)
}
async getNotes(eventNotes){
// THIS ALERT FIRES BEFORE PROMISES IN PARENT ARE COMPLETED
alert(`Notes.getNotes CALL.. ${eventNotes}`) // eventNotes = undefined
this.eventChanges = await eventNotes.map(note => {
return {
eventInfo: {
name: note.name,
group: note.groupNo || null,
date: note.displayDate,
},
note: note.noteToPresenter
}
})
}
...
I am relatively new to Vue so forgive me if I am overlooking something basic. I have been trying to fix it for a couple of days now and can't figure it out so any help is much appreciated!
If you are new to Vue, I really recommend reading the entire documentation of it and the tools you are using - vue-class-component (which is Vue plugin adding API for declaring Vue components as classes)
Caveats of Class Component - Always use lifecycle hooks instead of constructor
So instead of using constructor() you should move your code to created() lifecycle hook
This should be enough to fix your code in this case BUT only because the usage of the Notes component is guarded by v-if="notes.length" in the Parent - the component will get created only after notes is not empty array
This is not enough in many cases!
created() lifecycle hook (and data() function/hook) is executed only once for each component. The code inside is one time initialization. So when/if parent component changes the content of notesArr prop (sometimes in the future), the eventChanges will not get updated. Even if you know that parent will never update the prop, note that for performance reasons Vue tend to reuse existing component instances when possible when rendering lists with v-for or switching between components of the same type with v-if/v-else - instead of destroying existing and creating new components, Vue just updates the props. App suddenly looks broken for no reason...
This is a mistake many unexperienced users do. You can find many questions here on SO like "my component is not reactive" or "how to force my component re-render" with many answers suggesting using :key hack or using a watcher ....which sometimes work but is almost always much more complicated then the right solution
Right solution is to write your components (if you can - sometimes it is not possible) as pure components (article is for React but the principles still apply). Very important tool for achieving this in Vue are computed propeties
So instead of introducing eventChanges data property (which might or might not be reactive - this is not clear from your code), you should make it computed property which is using notesArr prop directly:
get eventChanges() {
return this.notesArr.map(note => {
return {
eventInfo: {
name: note.name,
group: note.groupNo || null,
date: note.displayDate,
},
note: note.noteToPresenter
}
})
}
Now whenever notesArr prop is changed by the parent, eventChanges is updated and the component will re-render
Notes:
You are overusing async. Your getNotes function does not execute any asynchronous code so just remove it.
also do not mix async and then - it is confusing
Either:
const promisesArray = [this.loadPrivate(),this.loadPublic()]
await Promise.all(promisesArray)
await this.checkAttendanceForPreviousTwoWeeks()
const results = await this.getCurrentParticipants()
this.currentP = results
this.notesArr = this.notes
or:
const promisesArray = [this.loadPrivate(),this.loadPublic()]
Promise.all(promisesArray)
.then(() => this.checkAttendanceForPreviousTwoWeeks())
.then(() => this.getCurrentParticipants())
.then((results) => {
this.currentP = results
this.notesArr = this.notes
})
Great learning resource

Using Variable from Props vs Passing Prop as Argument in React

In terms of writing components, which would be the preferred way to write below component? Assume that removeCard is outside of shown scope, ie. redux action.
My assumption would be that ComponentCardB would be, as it avoids passing an unnecessary argument which would be in the scope anyway. I imagine in terms of performance in the grand scheme of things, the difference is negligible, just more of a query in regards to best practise.
TIA
const ComponentCardA = (id) => {
const handleRemove = (cardId) => {
removeCard(cardId);
};
<div onClick={() => handleRemove(id)} />;
};
const ComponentCardB = (id) => {
const handleRemove = () => {
removeCard(id);
};
<div onClick={handleRemove} />;
};
With functional components like that, yes, there's no reason for the extra layer of indirection in ComponentCardA vs ComponentCardB.
Slightly tangential, but related: Depending on what you're passing handleRemove to and whether your component has other props or state, you may want to memoize handleRemove via useCallback or useMemo. The reason is that if other props or state change, your component function will get called again and (with your existing code) will create a new handleRemove function and pass that to the child. That means that the child has to be updated or re-rendered. If the change was unrelated to id, that update/rerender is unnecessary.
But if the component just has id and no other props, there's no point, and if it's just passing it to an HTML element (as opposed to React component), there's also probably no point as updating that element's click handler is a very efficient operation.
The second option is better way because using an arrow function in render creates a new function each time the component renders, which may break optimizations based on strict identity comparison.
Also if you don't want to use syntax with props.id you rather create function component with object as parameter:
const Component = ({id}) => { /* ... */ }
Of course using arrow function is also allowed but remember, when you don't have to use them then don't.

Is it possible to use references as react component's prop or state?

I want to create react table component which values are derived from single array object. Is it possible to control the component from view side? My goal is that every user using this component in their web browsers share the same data via singleton view object.
Program modeling is like below.
Database - there are single database in server which contain extinct and independent values.
DataView - there are singleton View class which reflects Database's table and additional dependent data like (sum, average)
Table - I'll build react component which looks like table. And it will show View's data with supporting sorting, filtering, editing and deleting row(s) feature (and more). Also it dose not have actual data, only have reference of data from View(Via shallow copy -- This is my question, is it possible?)
My intentions are,
- When user changes value from table, it is queried to DB by View, and if succeed, View will refer updated data and change it's value to new value and notify to Table to redraw it's contents. -- I mean redraw, not updating value and redraw.
- When values in View are changed with DB interaction by user request, there are no need to update component's value cause the components actually dose not have values, only have references to values (Like C's pointer). So only View should do is just say to Component to redraw it's contents.
I heard that React's component prop should be immutable. (Otherwise, state is mutable) My goal is storing references to component's real value to it's props so that there are no additional operation for reflecting View's data into Table.
It is concept problems, and I wonder if it is possible. Since javascript dose not support pointer officially(Am I right?), I'm not sure if it is possible.
View class is like below,
const db_pool = require('instantiated-singleton-db-pool-interface')
class DataView {
constructor() {
this.sessions = ['user1', 'user2'] // Managing current user who see the table
this.data = [ // This is View's data
{id:1, name:'James', phone:'12345678', bank:2000, cash:300, total:2300,..},
{id:2, name:'Michael', phone:'56785678', bank:2500, cash:250, total:2300,..},
{id:3, name:'Tyson', phone:'23455432', bank:2000, cash:50, total:2300,..}
] // Note that 'total' is not in db, it is calculated --`dependent data`
}
notifySessionToUpdate(ids) {
// ids : list of data id need to be updated
this.sessions.forEach((session) => {
session.onNotifiedUpdateRow(ids) // Call each sessions's
})
}
requestUpdateRow(row, changed_value) {
// I didn't write async, exception related code in this function for simple to see.
update_result = db_pool.update('UPDATE myTable set bank=2500 where id=1')
if (update_result === 'fail') return; // Do Nothing
select_result = db_pool.select('SELECT * from myTable where id=1') // Retrieve updated single data which object scheme is identical with this.data's data
for (k in Object.keys(select_result)) {.ASSIGN_TO_row_IF_VALUE_ARE_DIFFERENT.} // I'm not sure if it is possible in shallow copy way either.
calc.reCalculateRow(row) // Return nothing just recalculate dependant value in this.data which is updated right above.
// Notify to session
this.notifySessionToUpdate([1]) // Each component will update table if user are singing id=1's data if not seeing, it will not. [1] means id:1 data.
return // Success
}
... // other View features
}
Regarding session part, I'm checking how to implement sessionizing(?) the each user and it's component who is communicating with server. So I cannot provide further codes about that. Sorry. I'm considering implementing another shallow copied UserView between React Component Table and DataView(And also I think it helps to do something with user contents infos like sorting preference and etc...)
Regarding DB code, it is class which nest it's pool and query interface.
My problem is that I'm not familiar with javascript. So I'm not sure shallow copy is actually implementable in all cases which I confront with.
I need to think about,
1. Dose javascript fully support shallowcopy in consistent way? I mean like pointer, guarantee check value is reference or not.
2. Dose react's component can be used like this way? Whether using props or state Can this be fullfilled?
Actually, I strongly it is not possible to do that. But I want to check your opinions. Seems it is so C language-like way of thinking.
Redraw mean re-render. You can expose setState() or dispatch() functions from Table component and call them on View level using refs:
function View() {
const ref = useRef();
const onDbResponse = data => ref.current.update(data);
return (
<Table ref={ ref } />
);
}
const Table = React.forwardRef((props, ref) => {
const [ data, setData ] = useState([]);
useImperativeHandler(ref, {
update: setData
});
...
});
Anyway i don't think it's a good practice to update like that. Why can't you just put your data in some global context and use there?
const Context = React.createContext({ value: null, query: () => {} });
const Provider = ({ children }) => {
const [ value, setValue ] = useState();
const query = useCallback(async (request) => {
setValue(await DB.request(request));
}, [ DB ]);
const context = { value, query };
return <Context.Provider value={ context }>{ children }</Context.Provider>;
}
const useDB = () => useContext(Context);
const View = () => {
const { request } = useDB();
request(...);
}
const Table = () => {
const { value } = useDB();
...
}

When to really use getDerivedStateFromProps?

I'm having trouble determining if my component hierarchy really needs getDerivedStateFromProps, if the cases where it is needed is really as rare as the documentation makes it sound. It might be a fundamental misunderstanding about React/Redux design.
class AttributeList extends React.Component {
constructor(props){
super(props)
this.state = {
attributes: props.attributes,
newAttributes: []
}
}
addNewAttribute = () => {
// add new empty attribute to newAttributes state
}
onKeyChange = () => {
// update appropriate attribute key
}
onValueChange = () => {
// update appropriate attribute value
}
saveAttributes = () => {
// save the, API call
}
render = () => {
this.state.attributes.map((pair) => {
<Attribute
//pass data + functions, functional component />
})
this.state.newAttributes.map((pair) => {
<Attribute
//pass data + functions, functional component />
})
}
static getDerivedStateFromProps(){
// ?? do comparisons here to choose to remove or keep certain newAttributes? or just ignore result of save and keep interface as-is, just show error message if saving failed.
}
}
I have a parent component AttributeList which renders a bunch of Attributes, which are essentially key-value pairs. AttributeList receives the list of attributes of a document as props. However, the attributes can be edited, so it initializes its state (this.state.attributes) with this.props.attributes. Normally keys are immutable, but if a user adds a new attribute to the list, he can edit both the key and value. At any point, a user can save all the attributes. When the new attributes are saved, I'd like to disabled editing the keys for them as well. Here is the dilemma.
Option one is to save the document and just hope it worked, and then clear the new attributes list and mark all the attributes as saved (disabling the key input). I think this would be the "fully uncontrolled" solution, where once the state is initialized the component deals with everything on it's own. However, what if the save fails? I don't want to show and incorrect state to the user.
So I want to do option two. After save, fetch the document, which will load the attribute list and re-render the component. However I need to get rid of my new attributes since they are now a part of the attributes prop. I would like to verify that the new attributes are actually a part of the attributes prop now. It seems like this would happen ingetDerivedStateFromProps where I would on each render cycle check if any new attribute keys already exist in the attributes prop, and remove them from the "new" list if they do, and return that state.
But is this really the right time to use getDerivedStateFromProps? It seems to me that for any page that a user is "editing" something where you make an API call to save it, if you want to render based on the saved data ("the truth"), then I need to use getDerivedStateFromProps. Or perhaps from a design perspective it is better to show a message akin to "data not successfully saved" and keep the state as is, to prevent any data loss. I'm honestly not sure.
I don't see how getDerivedStateFromProps comes into it as there's no reason you need to copy props into state is there? When an old attribute value is changed you save it to the redux store, when new attribute properties are changed you can update local state (or save them to a different slice of the store, or differentiate them some other way). Update rules can be enforced in the update handlers or during merge on save.
// dispatch redux action to update store
onOldValueChange = () => {}
// this.setState to update new value
onNewKeyChange = () => {}
onNewValueChange = () => {}
render = () => {
this.props.attributes.map((pair) => {
<Attribute
//pass data + onOldValueChange, functional component />
})
this.state.newAttributes.map((pair) => {
<NewAttribute
//pass data + functions, functional component />
})
}

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