Angular 4: reactive form control is stuck in pending state with a custom async validator : <p>I am building an Angular 4 app that requires the BriteVerify email validation on form fields in several components. I am trying to implement this validation as a custom async validator that I can use with reactive forms. Currently, I can get the API response, but the control status is stuck in pending state. I get no errors so I am a bit confused. Please tell me what I am doing wrong. Here is my code. </p>

<h2>Component</h2>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>import { Component, 
         OnInit } from '@angular/core';
import { FormBuilder, 
         FormGroup, 
         FormControl, 
         Validators } from '@angular/forms';
import { Router } from '@angular/router';

import { EmailValidationService } from '../services/email-validation.service';

import { CustomValidators } from '../utilities/custom-validators/custom-validators';

@Component({
    templateUrl: './email-form.component.html',
    styleUrls: ['./email-form.component.sass']
})

export class EmailFormComponent implements OnInit {

    public emailForm: FormGroup;
    public formSubmitted: Boolean;
    public emailSent: Boolean;
    
    constructor(
        private router: Router,
        private builder: FormBuilder,
        private service: EmailValidationService
    ) { }

    ngOnInit() {

        this.formSubmitted = false;
        this.emailForm = this.builder.group({
            email: [ '', [ Validators.required ], [ CustomValidators.briteVerifyValidator(this.service) ] ]
        });
    }

    get email() {
        return this.emailForm.get('email');
    }

    // rest of logic
}</code></pre>
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</p>

<h2>Validator class</h2>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>import { AbstractControl } from '@angular/forms';

import { EmailValidationService } from '../../services/email-validation.service';

import { Observable } from 'rxjs/Observable';

import 'rxjs/add/observable/of';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/debounceTime';
import 'rxjs/add/operator/distinctUntilChanged';

export class CustomValidators {

    static briteVerifyValidator(service: EmailValidationService) {
        return (control: AbstractControl) =&gt; {
            if (!control.valueChanges) {
                return Observable.of(null);
            } else {
                return control.valueChanges
                    .debounceTime(1000)
                    .distinctUntilChanged()
                    .switchMap(value =&gt; service.validateEmail(value))
                    .map(data =&gt; {
                        return data.status === 'invalid' ? { invalid: true } : null;
                    });
            }
        }
    }
}</code></pre>
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</p>

<h2>Service</h2>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>import { Injectable } from '@angular/core';
import { HttpClient,
         HttpParams } from '@angular/common/http';

interface EmailValidationResponse {
    address: string,
    account: string,
    domain: string,
    status: string,
    connected: string,
    disposable: boolean,
    role_address: boolean,
    error_code?: string,
    error?: string,
    duration: number
}

@Injectable()
export class EmailValidationService {

    public emailValidationUrl = 'https://briteverifyendpoint.com';

    constructor(
        private http: HttpClient
    ) { }

    validateEmail(value) {
        let params = new HttpParams();
        params = params.append('address', value);
        return this.http.get&lt;EmailValidationResponse&gt;(this.emailValidationUrl, {
            params: params
        });
    }
}</code></pre>
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<h2>Template (just form)</h2>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;form class="email-form" [formGroup]="emailForm" (ngSubmit)="sendEmail()"&gt;
    &lt;div class="row"&gt;
        &lt;div class="col-md-12 col-sm-12 col-xs-12"&gt;
            &lt;fieldset class="form-group required" [ngClass]="{ 'has-error': email.invalid &amp;&amp; formSubmitted }"&gt;
                &lt;div&gt;{{ email.status }}&lt;/div&gt;
                &lt;label class="control-label" for="email"&gt;Email&lt;/label&gt;
                &lt;input class="form-control input-lg" name="email" id="email" formControlName="email"&gt;
                &lt;ng-container *ngIf="email.invalid &amp;&amp; formSubmitted"&gt;
                    &lt;i class="fa fa-exclamation-triangle" aria-hidden="true"&gt;&lt;/i&gt;&amp;nbsp;Please enter valid email address.
                &lt;/ng-container&gt;
            &lt;/fieldset&gt;
            &lt;button type="submit" class="btn btn-primary btn-lg btn-block"&gt;Send&lt;/button&gt;
        &lt;/div&gt;
    &lt;/div&gt;
&lt;/form&gt;</code></pre>
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