Fix Error: Cannot read properties of undefined (reading 'pipe') in NestJS

This error occurs in a NestJS interceptor when the route handler does not return an Observable, typically because it returns void or a raw value instead. Interceptors expect next.handle() to return an Observable. Fix it by ensuring all intercepted handlers return a value and wrapping non-Observable returns with of().

Reading the Stack Trace

Here's what each line means:

• at LoggingInterceptor.intercept (src/interceptors/logging.interceptor.ts:18:35): Your interceptor at line 18 calls .pipe() on the result of next.handle(), but it returned undefined because the handler has no return value.
• at InterceptorsConsumer.intercept (node_modules/@nestjs/core/interceptors/interceptors-consumer.js:22:36): NestJS's interceptor consumer runs all registered interceptors around the handler execution.
• at /node_modules/@nestjs/core/router/router-execution-context.js:46:28: The router execution context wraps the handler call and pipes through interceptors before sending the response.

Common Causes

@Post('notify')
async sendNotification(@Body() dto: NotifyDto) {
  await this.notificationService.send(dto);
  // No return value - returns undefined
}

intercept(context: ExecutionContext, next: CallHandler) {
  return next.handle().pipe(
    tap(() => console.log('After...')),
  );
  // Crashes if next.handle() returns undefined
}

@Get('download')
download(@Res() res: Response) {
  res.sendFile('/path/to/file'); // Bypasses interceptors
}

The Fix

Check whether next.handle() returns a valid Observable before calling .pipe(). If the handler returned void or a non-Observable value, wrap it with of() to create a valid Observable that the interceptor pipeline can process.

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { tap } from 'rxjs/operators';

@Injectable()
export class LoggingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    const now = Date.now();
    return next.handle().pipe(
      tap(() => console.log(`Request took ${Date.now() - now}ms`)),
    );
  }
}

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable, of } from 'rxjs';
import { tap } from 'rxjs/operators';

@Injectable()
export class LoggingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    const now = Date.now();
    const result = next.handle();

    if (!result || typeof result.pipe !== 'function') {
      console.log(`Request took ${Date.now() - now}ms`);
      return result ? of(result) : of(undefined);
    }

    return result.pipe(
      tap(() => console.log(`Request took ${Date.now() - now}ms`)),
    );
  }
}

Testing the Fix

import { LoggingInterceptor } from './logging.interceptor';
import { of } from 'rxjs';
import { ExecutionContext, CallHandler } from '@nestjs/common';

describe('LoggingInterceptor', () => {
  let interceptor: LoggingInterceptor;
  const mockContext = {} as ExecutionContext;

  beforeEach(() => {
    interceptor = new LoggingInterceptor();
  });

  it('logs request duration for normal handlers', (done) => {
    const consoleSpy = jest.spyOn(console, 'log').mockImplementation();
    const handler: CallHandler = { handle: () => of({ data: 'test' }) };

    interceptor.intercept(mockContext, handler).subscribe((result) => {
      expect(result).toEqual({ data: 'test' });
      expect(consoleSpy).toHaveBeenCalledWith(expect.stringContaining('Request took'));
      consoleSpy.mockRestore();
      done();
    });
  });

  it('handles void handlers without crashing', (done) => {
    const handler: CallHandler = { handle: () => undefined as any };

    interceptor.intercept(mockContext, handler).subscribe((result) => {
      expect(result).toBeUndefined();
      done();
    });
  });
});

Run your tests:

npm test

Pushing Through CI/CD

git checkout -b fix/nestjs-interceptor-undefined,git add src/interceptors/logging.interceptor.ts src/interceptors/__tests__/logging.interceptor.spec.ts,git commit -m "fix: handle undefined return from next.handle() in interceptor",git push origin fix/nestjs-interceptor-undefined

Your CI config should look something like this:

name: CI
on:
  pull_request:
    branches: [main]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'
      - run: npm ci
      - run: npm test -- --coverage
      - run: npm run build

The Full Manual Process: 18 Steps

Here's every step you just went through to fix this one bug:

1. Notice the error alert or see it in your monitoring tool
2. Open the error dashboard and read the stack trace
3. Identify the file and line number from the stack trace
4. Open your IDE and navigate to the file
5. Read the surrounding code to understand context
6. Reproduce the error locally
7. Identify the root cause
8. Write the fix
9. Run the test suite locally
10. Fix any failing tests
11. Write new tests covering the edge case
12. Run the full test suite again
13. Create a new git branch
14. Commit and push your changes
15. Open a pull request
16. Wait for code review
17. Merge and deploy to production
18. Monitor production to confirm the error is resolved

Total time: 30-60 minutes. For one bug.

npm install bugstack-sdk

import { initBugStack } from 'bugstack-sdk'

initBugStack({ apiKey: process.env.BUGSTACK_API_KEY })

Deploying the Fix (Manual Path)

1. Update interceptors to handle undefined returns from next.handle().
2. Ensure all intercepted handlers return a value.
3. Avoid using @Res() in routes with interceptors.
4. Run tests to verify interceptor behavior.
5. Open a PR, merge after CI, and verify in staging.

Frequently Asked Questions