Cross Control Validation Angular Forms

crossControlValidation.js

let input1$ = this.form.controls.input1.valueChanges;
let input2$ = this.form.controls.input2.valueChanges;
let input3$ = this.form.controls.input3.valueChanges;

combineLatest(input1$, input2$, input3$)
    .do(([input1, input2, input3]) => {
        this.form.controls.input1.clearAsyncValidators();
    })
    .debounceTime(500)
    .subscribe(([input1, input2, input3]) => {
    
    if (!input1 || !input2 || !input3) return null;
    
    let request = {
        input1,
        input2,
        input3
    }

    const inputValidatorFn = this.getEftValidator(request);
    this.form.controls.input1.setAsyncValidators(inputValidatorFn);
    this.form.controls.input1.updateValueAndValidity();
    
});

private getEftValidator(request): ValidatorFunction {
    return ( control: FormGroup ) => {
        return new Promise((resolve, reject) => {
    
            this.someService.validateEft(request)
                .subscribe((serviceResponse)=>{
                    let response = serviceResponse.json();
                    if( response && response.data.valid ) return resolve(null);
                    if( response && !response.data.valid ) {
                        if( response.data.reason === 'reason1' )resolve({reason1: 'more info about error'})
                        if( response.data.reason === 'reason2') resolve({reason2: 'more info about error'})
                    }
                })
                .catch(err=>handleError(err));
        })
    }
}