Tips for waiting for an Http response in TypeScript with Angular 5

Question

Tips for waiting for an Http response in TypeScript with Angular 5

Is it possible to create a function that can retrieve a token from a server, considering that the http.post() method generates a response after the function has already returned the token?

How can I ensure that my function waits for the http.post() call to complete before returning the token?

This is the code snippet in question:

import { Injectable } from '@angular/core';
import { Http } from '@angular/http';

@Injectable()

export class ServerConnectionService{
    constructor( private http : Http) { }
    token : string;
    Login(Password : string, Username : string, ServerRootURL : string) : string
    {
        let url = ServerRootURL + "api/AdminApp/RegisterToken";
        this.http.post(url, { "Username": Username, "Password": Password }).toPromise()
            .then(res => this.token =  res.json())
            .catch(msg => console.log('Error: ' + msg.status + ' ' + msg.statusText))
        return this.token;
    }
}

Your help and suggestions are greatly appreciated.

typescript http angular5

Answer 1

Answer №1

When dealing with asynchronous code, you cannot simply wait for it to finish and return a value immediately. By utilizing promises, you must utilize functions that can be executed once the promise is resolved, such as the then function. This allows you to write logic that depends on the result of the promise inside these then functions. In your scenario, it would look like this:

Login(Password: string, Username: string, ServerRootURL: string): Promise<string> {
    let url = ServerRootURL + "api/AdminApp/RegisterToken";
    return this.http.post(url, { "Username": Username, "Password": Password }).toPromise()
        .then(res => this.token = res.json())
        .catch(msg => console.log('Error: ' + msg.status + ' ' + msg.statusText))
}

To use this function, you would call it like so:

Login('password', 'username', 'http://localhost:8081').then(token => your logic here)

Answer 2

When dealing with asynchronous code, you cannot simply wait for it to finish and return a value immediately. By utilizing promises, you must utilize functions that can be executed once the promise is resolved, such as the then function. This allows you to write logic that depends on the result of the promise inside these then functions. In your scenario, it would look like this:

Login(Password: string, Username: string, ServerRootURL: string): Promise<string> {
    let url = ServerRootURL + "api/AdminApp/RegisterToken";
    return this.http.post(url, { "Username": Username, "Password": Password }).toPromise()
        .then(res => this.token = res.json())
        .catch(msg => console.log('Error: ' + msg.status + ' ' + msg.statusText))
}

To use this function, you would call it like so:

Login('password', 'username', 'http://localhost:8081').then(token => your logic here)

Answer 3

Answer №2

If you define your Login() function as async, you can then use the await keyword to wait for the http.post() call:

public async Login(password: string, username: string): string {
    ...
    let response: Response = await this.http.post(url, data).toPromise();
    return response.json();
}

Keep in mind that when calling the Login() function, you will also need to use await:

let authToken = await Login("foo", "bar");

Answer 4

If you define your Login() function as async, you can then use the await keyword to wait for the http.post() call:

public async Login(password: string, username: string): string {
    ...
    let response: Response = await this.http.post(url, data).toPromise();
    return response.json();
}

Keep in mind that when calling the Login() function, you will also need to use await:

let authToken = await Login("foo", "bar");

Tips for waiting for an Http response in TypeScript with Angular 5

Answer №1

Answer №2

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