I am trying to pass data to a child component and I keep getting an undefined prop. I think it may have an issue with when Im setting the state in the parent component. Should i not be using componentWillMount?
export default class AllItems extends Component {
constructor () {
super()
this.state=({ user: cookie.load('user')})
this.httpHandler = axios.create({
baseURL: 'http://localhost:3000/',
headers: {
'Authorization': this.state.user.token
}
})
}
componentWillMount() {
this.httpHandler('/products/')
.then(function (response) {
this.setState({ winks: response.data.data})
console.log(this.state.winks)
}.bind(this))
}
render() {
return (
<Winks products={this.state.winks} />
)
}
}
The problem is that your promise may not return before componentWillMount finishes and render is called. So products won't exist yet. You could do something like this:
render() {
if (this.state.winks) {
return (<Winks products={this.state.winks} />)
} else {
return (<div>No Winks yet</div>);
}
}
the problem is that you do not have an initial state for winks Since you are relying on an ajax call to set the state of winks, the ajax call will take place asynchronously and then it will execute the render function before the api call finishes causing this.state.winks to be undefined initially.
You could do something like this
render() {
let content = this.state.winks ? <Winks products={this.state.winks} /> : <div/>
return <div> {content} </div>
Related
I am trying to display a routerlink name based on a condition. I want to display the div section routerLink name if condition is true.If i check {{isNameAvailable}}, first it displays false and after this.names got the values it shows true.Since in the component getDetails() method is asynchronous this.names getting the values after html template render.Therefore this routerLink does n't display.Therefore I want to display div section after some time. (That 's the solution i have) Don't know whether is there any other solution.
This is my html file code.
<main class="l-page-layout ps-l-page-layput custom-scroll bg-white">
{{isNameAvailable}}
<div class="ps-page-title-head" >
<a *ngIf ="isNameAvailable === true" [routerLink]="['/overview']">{{Name}}
</a>
{{Name}}
</div>
</main>
This is my component.ts file
names= [];
isNameAvailable = false;
ngOnInit() {
this.getDetails()
}
getDetails() {
this.route.params.subscribe(params => {
this.names.push(params.Names);
console.log(this.names);
this.getValues().then(() => {
this.isNameAvailable = this.checkNamesAvailability(this.names);
console.log(this.isNameAvailable);
});
});
}
resolveAfterSeconds(x) {
return new Promise(resolve => {
setTimeout(() => {
resolve(x);
}, 900);
});
}
checkNamesAvailability(names) {
console.log(names);
return names.includes('Sandy');
}
async getValues() {
await this.resolveAfterSeconds(900);
}
And console.log(this.isLevelAvailable); also true. What I can do for this?
1.You do not have anything to show in the HTML only the isNameAvailable, because you do not have any assignment in the Name variable.
2.It is better to use the angular build-in async pipe,
when you want to show the returned value from observables.
3.When you are using the *ngIf directive you can skip *ngIf ="isNameAvailable === true" check because the variable is boolean type, you gust write *ngIf ="isNameAvailable", it will check also for null but NOT for undefined
It is working because the *ngIf directive is responsible for checking and rendering the UI, you can see how many times the directive is checking by calling an function and print and answer in the console.
By any chance do you have changeDetection: ChangeDetectionStrategy.OnPush docs set in component annotation? That might explain this behaviour. With it Angular run change detection only on component #Input()'s changes and since in your case there were non it did not run change detection which is why template was not updated. You could comment that line to check if that was cause of the issue. You are always able to run change detection manually via ChangeDetectorRef.detectChange() docs which should solve you problem
constructor(private cd: ChangeDetectorRef) {}
...
getDetails() {
this.route.params.subscribe(params => {
...
this.getValues().then(() => {
this.isNameAvailable = this.checkNamesAvailability(this.names);
this.cd.detectChanges(); // solution
console.log(this.isNameAvailable);
});
});
}
This stackblitz show this bug and solution. You can read more about change detection here
You could use RxJS timer function with switchMap operator instead of a Promise to trigger something after a specific time.
Try the following
import { Subject, timer } from 'rxjs';
import { takeUntil, switchMap } from 'rxjs/operators';
names= [];
isNameAvailable = false;
closed$ = new Subject();
ngOnInit() {
this.getDetails()
}
getDetails() {
this.route.params.pipe(
switchMap((params: any) => {
this.names.push(params.Names);
return timer(900); // <-- emit once after 900ms and complete
}),
takeUntil(this.closed$) // <-- close subscription when `closed$` emits
).subscribe({
next: _ => {
this.isNameAvailable = this.checkNamesAvailability(this.names);
console.log(this.isNameAvailable);
}
});
}
checkNamesAvailability(names) {
console.log(names);
return names.includes('Sandy');
}
ngOnDestroy() {
this.closed$.next(); // <-- close open subscriptions when component is closed
}
I am trying to subscribe Observable in a function. But it is not triggering.
resetShippingForm(): void {
this.resetForm$ =
this.assemblyItemService.resetSUForm$.asObservable();
this.resetForm$.subscribe(data => {
if (data) {
console.log(data);
}
});
}
Make sure resetSUForm subject observer is feed value using next(value) method and call resetShippingForm() inside constructor/ngOnInit.
I am trying to run getResponse once when a web components finishes loading. However, when I try to run this, the debounce function just acts as an async delay and runs 4 times after 5000 ms.
static get properties() {
return {
procedure: {
type: String,
observer: 'debounce'
}
}
}
debounce() {
this._debouncer = Polymer.Debouncer.debounce(this._debouncer, Polymer.Async.timeOut.after(5000), () => {
this.getResponse();
});
}
getResponse() {
console.log('get resp');
}
What is necessary to get getResponse to run once upon the loading of the element?
Are you sure you want to use a debouncer for that? you could just use the connectedCallBack to get a one Time Event
class DemoElement extends HTMLElement {
constructor() {
super();
this.callStack = 'constructor->';
}
connectedCallback() {
this.callStack += 'connectedCallback';
console.log('rendered');
fetch(this.fakeAjax()).then((response) => {
// can't do real ajax request here so we fake it... normally you would do
// something like this.innerHTML = response.text();
// not that "rendered" get console logged before "fetch done"
this.innerHTML = `
<p>${this.callStack}</p>
<p>${response.statusText}</p>
`;
console.log('fetch done');
}).catch(function(err) {
console.log(err); // Error :(
});
}
fakeAjax() {
return window.URL.createObjectURL(new Blob(['empty']));
};
}
customElements.define('demo-element', DemoElement);
<demo-element></demo-element>
If you really need to use an observer you could also set a flag this.isLoaded in your connectedCallback() and check for that in your observer code.
I have some URL with json and need to read data.
For the sake of this example json looks like this:
{
"results": [
...
],
"info": {
...
}
}
I want to return fetched data as a property of a component.
What is the best way to do it?
I tried to do that with axios. I managed to fetch data, but after setState in render() method I received an empty object. This is the code:
export default class MainPage extends React.Component {
constructor(props: any) {
super(props);
this.state = {
list: {},
};
}
public componentWillMount() {
axios.get(someURL)
.then( (response) => {
this.setState({list: response.data});
})
.catch( (error) => {
console.log("FAILED", error);
});
}
public render(): JSX.Element {
const {list}: any = this.state;
const data: IScheduler = list;
console.log(data); // empty state object
return (
<div className="main-page-container">
<MyTable data={data}/> // cannot return data
</div>
);
}
}
I don't have a clue why in render() method the data has gone. If I put
console.log(response.data);
in .then section, I get the data with status 200.
So I ask now if there is the other way to do that.
I would be grateful for any help.
----Updated----
In MyTable component I got an error after this:
const flightIndex: number
= data.results.findIndex((f) => f.name === result);
Error is:
Uncaught TypeError: Cannot read property 'findIndex' of undefined
What's wrong here? How to tell react this is not a property?
Before the request is returned, React will try to render your component. Then once the request is completed and the data is returned, react will re-render your component following the setState call.
The problem is that your code does not account for an empty/undefined data object. Just add a check, i.e.
if (data && data.results) {
data.results.findIndex(...);
} else {
// display some loading message
}
In React, after you have stored your ajax result in the state of the component (which you do appear to be doing), you can retrieve that result by calling this.state.list
So to make sure this is working properly, try <MyTable data={this.state.list}>
https://daveceddia.com/ajax-requests-in-react/
I'm a bit disappointed of my results about getting started with reactjs.
I'm now just trying to parse json data from a simple restful ws.
If I put on chrome the url of rest get query, it answers correctly a json array:
[{"label":"TestLabel!!","value":7,"rating":17.25},{"label":"TestLabel2 !!","value":8,"rating":18.25}]
this is my React component:
export default class ItemLister extends React.Component {
constructor() {
super();
this.state = { items: [{"label":"Test1!!","value":7,"rating":17.25}] };
}
componentDidMount() {
fetch('/rest/json/product/get')
.then(result=> {
this.state.items.push(result);
});
}
render() {
return(
<div>
<div>Items:</div>
{
this.state.items.map(function(item, i){
return <div key={i}>{item.label}</div>
}
)}
</div>
);
}
}
This, after lots of tweaking, shows no errors, but nothing happens to the list, which shows only the constructor element.
Pls point me to the right direction...
thanks
SOLVED:
the "setState()" as suggested was part of the problem.
The other part is the way i manage the json answer.
This way the project works:
componentDidMount() {
fetch('/rest/json/product/get')
.then(response => response.json())
.then(response => {
this.setState({items: response });
})
}
But I just tried another way to implement the call by chance since i was totally lost.
I feel a bit confused. What is the correct way to implement a fetch?
Anyways...this is ok.
Read the last line in the Docs:
Never mutate this.state directly, as calling setState() afterwards may replace the mutation you made. Treat this.state as if it were immutable.
try this:
this.setState((state) => ({ items: state.items.concat(result) }))
or you can do this if result is array:
this.setState({ items: [...this.state.items , ...result] })
try this.setState('items',result)