Here is my Objective.
@Component({
selector: "data",
template: "<h1>{{ fetchData() }}</h1>"
})
export class DataComponent{
this.http.get(path).subscribe({
res => return res;
})
}
In the scenario where fetchData was invoked within the DataComponent, You might recommend storing it in a variable such as this.data = res and accessing it as {{data}}.However, I have a specific requirement to use it as {{fetchData}}. Any suggestions on how to achieve this?
Returning the value directly is not possible due to the asynchronous nature of the call. An async call runs in the background (scheduled for later execution) while your code continues.
It's important to note that such code cannot be placed directly in the class; it should be moved into a method or the constructor instead.
One workaround is to avoid directly calling subscribe() and instead use an operator like map().
export class DataComponent{
someMethod() {
return this.http.get(path).map(res => {
return res.json();
});
}
}
Furthermore, you can chain multiple .map calls with the same Observables for better code clarity and separation. For example:
validateResponse = (response) => validate(response);
parseJson = (json) => JSON.parse(json);
fetchUnits() {
return this.http.get(requestUrl).map(this.validateResponse).map(this.parseJson);
}
This approach allows the observable to be returned for subscription by the caller.
export class DataComponent{
someMethod() {
return this.http.get(path).map(res => {
return res.json();
});
}
otherMethod() {
this.someMethod().subscribe(data => this.data = data);
}
}
The subscriber can also be located in another class for brevity.
data => this.data = data
and
res => return res.json()
are arrow functions, similar to normal functions. These functions are passed to subscribe(...) or map(...) to be executed once data arrives from the observable response.
This explains why data cannot be returned directly, as it may not have been received yet when someMethod() completes.
There are two methods I am aware of:
export class SomeComponent implements OnInit
{
public localVar:any;
ngOnInit(){
this.http.get(Path).map(res => res.json()).subscribe(res => this.localVar = res);
}
}
With this approach, the result will be stored in a local variable once the information is retrieved similar to a promise. You can then display it using {{ localVar }}
Another option is to assign an observable as a local variable.
export class SomeComponent
{
public localVar:any;
constructor()
{
this.localVar = this.http.get(path).map(res => res.json());
}
}
By doing this, you make an observable accessible and in your HTML, you can utilize AsyncPipe like this: {{ localVar | async }}
Please give these methods a try and let me know if they work for you. Also, feel free to provide feedback if there are any issues since Angular 2 is relatively new.
I hope this explanation proves helpful.
What if we save this in a variable that is accessible outside of the subscribe function?
let updatedData = this.bindPlusService.getJSONCurrentRequestData(submission).map(data => {
return delete JSON.parse(data)['$id'];
});
To fetch data in Angular, you can utilize the pipe operator and subscribe to getData() method or use the async pipe in the template as shown below:
template.html
<h1>{{ data$ | async }}</h1>
component.ts
data$ = this.apiService.getData();
api.service.ts
getData() {
return this._http
.get(url)
.pipe(
map((res: any) => {
return res;
// or if you want to transform data
// return transformRes(res);
})
);
}
transformRes(res) {return ...transform logic.}
I have employed this method numerous times...
@Component({
selector: "info",
template: "<h2>{{ displayInfo() }}</h2>"
})
export class InfoComponent{
this.http.get(url).subscribe({
InfoComponent.setSubscriptionData(response);
})
}
static subscriptionData:any;
static setSubscriptionData(data):any{
InfoComponent.subscriptionData=data;
return data;
}Utilize the static keyword and streamline your workflow... you can either utilize a static variable or directly return the desired object.... I trust this will be beneficial for you.. enjoy coding...
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