rxjs7

RxJS 6 → 7 Migration Guide

toPromise() Replacement

toPromise() is deprecated in RxJS 7. Scan all .ts files for .toPromise() calls.

// OLD (RxJS 6)
const result = await this.http.get(url).toPromise();

// NEW (RxJS 7)
import { firstValueFrom } from 'rxjs';
const result = await firstValueFrom(this.http.get(url));

When to use which

• firstValueFrom: HTTP calls, one-shot observables (99% of cases in Angular)
• lastValueFrom: Only when you need the LAST value before complete

Detection

grep -r "\.toPromise()" --include="*.ts" src/ projects/

Other v7 Changes

throwError

// OLD
throwError('error message');

// NEW
throwError(() => new Error('error message'));

pluck (deprecated)

// OLD
source$.pipe(pluck('prop'));

// NEW
source$.pipe(map(x => x.prop));

Subject.create (removed)

// OLD
const subject = Subject.create(observer, observable);

// NEW
const subject = new Subject();

Import paths

Import paths are unchanged for most operators. The main change is:

• import { Observable } from 'rxjs' — still valid
• import { map, filter } from 'rxjs/operators' — still valid
• import { firstValueFrom, lastValueFrom } from 'rxjs' — NEW

Scheduler arguments (deprecated)

// OLD
of(1, 2, 3, asyncScheduler);

// NEW
scheduled([1, 2, 3], asyncScheduler);

Quick Scan Commands

# Count toPromise() calls
grep -rc "\.toPromise()" --include="*.ts" src/ projects/ | grep -v ":0"

# Count throwError with string
grep -rn "throwError(" --include="*.ts" src/ projects/ | grep -v "=>"

# Count pluck usage
grep -rc "pluck(" --include="*.ts" src/ projects/ | grep -v ":0"