We have defined an interface for error types:
export interface ErrorTypes {
[key: string]: string;
}
We want an Angular Component that can display an enumeration of error types defined by the ErrorTypes
interface when the components error$:Observable<string>
emits an error key.
For example we may implement the interface like this:
errorTypes: ErrorTypes = {
NETWORK_ERROR: "Network Error",
DATA_ERROR: "Data Error"
};
Note that the ErrorTypes
instance values will be used to display the type of error that occurred in the components template.
Create the dataError$:Observable<string> = of('DATA_ERROR')
.
And trigger data error display like this:
<fs-error [error$]="dataError$" [errorTypes]="errorTypes"></fs-error>
Approach
This is the complete implementation of our component:
import { Component, Input, OnInit } from "@angular/core";
import { Observable } from "rxjs";
import { ErrorTypes } from "./error.model";
@Component({
selector: "fs-error",
template: `
<ng-container *ngIf="(error$ | async)">
<div [ngSwitch]="error$ | async">
<ng-container *ngFor="let key of errorTypeKeys">
<div *ngSwitchCase="key">
<h3>{{ errorTypes[key] }}</h3>
</div>
</ng-container>
<div *ngSwitchDefault>The error key had no matches</div>
</div>
</ng-container>
`,
styles: []
})
export class ErrorComponent implements OnInit {
@Input()
error$: Observable<string>;
@Input()
errorTypes: ErrorTypes;
errorTypeKeys: string[];
ngOnInit() {
this.errorTypeKeys = Object.keys(this.errorTypes);
}
}
We render the error template if an error occurs:
<ng-container *ngIf="(error$ | async)">
...
</ng-container>
We generate the dynamic switch conditions like this:
<ng-container *ngFor="let key of errorTypeKeys">
<div *ngSwitchCase="key">
<h3>{{ errorTypes[key] }}</h3>
</div>
The error that occurred is displayed via this part of the template:
<h3>{{ errorTypes[key] }}</h3>
Dynamic generation of the string[]
array of possible error conditions ( this.errorTypeKeys
) is done by the ErrorComponent
inside the ngOnInit()
life cycle method:
this.errorTypeKeys = Object.keys(this.errorTypes);