Fetching a value from a URL in Angular 2 using promises and the await keyword

Looking to extract a value from the URL using promises and async/await, but encountering an issue where both Chrome and Opera seem to hang at that point. Can anyone steer me in the right direction or identify what I might be doing wrong?

My component implements: ngOnInit

Constructor:

constructor(private route: ActivatedRoute, 
            private zone : NgZone
            ) 
            {

            }

Imports:

import { Component, OnInit, NgZone } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Observable } from 'rxjs/Rx';

Methods:

async ngOnInit() 
{
    var Id : string = await this.getIdFromUrl(); 
}


getIdFromUrl() : Promise<string> 
    {
        return this.route.params.map(params => 
        {   
            return params['id']; 
        }).toPromise();  
    }

Answer №1

ngOnInit is meant to have a return type of void. Using async with it can lead to an XY problem, as detailed in the official documentation. A promise returned from an async ngOnInit may result in uncaught errors. Instead, promises that need to be resolved during initialization should be set up as resolvers.

The reason route.params is an observable is because it emits multiple values when navigating to the same route with different parameters. Trying to convert this observable to a promise using toPromise() will leave a pending promise, highlighting the difference between observables and promises.

When dealing with initial parameter values synchronously during component initialization, they can be accessed through the ActivatedRouteSnapshot interface.

ngOnInit() {
    const id: string = route.snapshot.params.id;
}

Depending on route usage and specific route reuse strategies, directly accessing params like this may not handle subsequent param changes correctly. In such cases, sticking to the route.params observable is generally recommended for consistency.

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