angular/angular-cli · error · Error

As of angular-devkit version 8.0, the "chokidar" package mus

Error message

As of angular-devkit version 8.0, the "chokidar" package must be installed in order to use watch() features.

What it means

The devkit's NodeJSAsyncHost/watch support uses chokidar's FSWatcher, which is treated as an optional peer dependency. loadFSWatcher tries require('chokidar'); if the require fails with MODULE_NOT_FOUND it throws this explanatory error telling you to install chokidar. (The odd message placement means any other require failure is rethrown as-is.) It exists because watch() features were moved to depend on an optional chokidar package in angular-devkit 8.0.

Source

Thrown at packages/angular_devkit/core/node/host.ts:47

    await fsPromises.access(path, constants.F_OK);

    return true;
  } catch {
    return false;
  }
}

// This will only be initialized if the watch() method is called.
// Otherwise chokidar appears only in type positions, and shouldn't be referenced
// in the JavaScript output.
let FSWatcher: typeof import('chokidar').FSWatcher;
function loadFSWatcher() {
  if (!FSWatcher) {
    try {
      FSWatcher = require('chokidar').FSWatcher;
    } catch (e) {
      if ((e as NodeJS.ErrnoException).code !== 'MODULE_NOT_FOUND') {
        throw new Error(
          'As of angular-devkit version 8.0, the "chokidar" package ' +
            'must be installed in order to use watch() features.',
          {
            cause: e,
          },
        );
      }
      throw e;
    }
  }
}

/**
 * An implementation of the Virtual FS using Node as the background. There are two versions; one
 * synchronous and one asynchronous.
 */
export class NodeJsAsyncHost implements virtualFs.Host<Stats> {
  get capabilities(): virtualFs.HostCapabilities {

View on GitHub (pinned to bb72145f9a)

Solutions

Install chokidar: npm install chokidar (a version compatible with your devkit major version)
If using pnpm/yarn PnP, add chokidar as an explicit dependency of the package using @angular-devkit/core
Re-enable optional dependency installation (drop --omit=optional) and reinstall

Example fix

// before
npm install @angular-devkit/core
// after
npm install @angular-devkit/core chokidar

Defensive patterns

Strategy: fallback

Validate before calling

let chokidarAvailable = false;
try { require.resolve('chokidar'); chokidarAvailable = true; } catch {}
if (!chokidarAvailable && needsWatch) {
  throw new Error('watch() requires chokidar: npm install chokidar');
}

Type guard

function hasChokidar(): boolean {
  try { require.resolve('chokidar'); return true; } catch { return false; }
}

Try / catch

try {
  const watcher = host.watch(path, options);
  // ...use watcher
} catch (e) {
  if ((e as Error).message.includes('chokidar')) {
    // fallback: polling with fs.watch / setInterval, or fail fast with install instructions
  } else { throw e; }
}

Prevention

Explicitly list chokidar in package.json dependencies of any package using @angular-devkit/core watch
Avoid npm install --omit=optional in environments that need watch features
With pnpm, use public-hoist-pattern or direct dependency to make chokidar resolvable
After devkit major upgrades, re-verify optional peer deps resolve from the consuming project

When it happens

Trigger: Calling watch() (or any API that watches the filesystem via the devkit node host) in a project where the chokidar package is not resolvable from node_modules.

Common situations: Upgrading angular-devkit from <8.0 where chokidar was bundled, pnpm/yarn strict dependency hoisting hiding chokidar, minimal installs (npm install --omit=optional) dropping chokidar, custom CLI tooling built on @angular-devkit/core without declaring chokidar.

Understand the failure class

Background: "X is not installed. Please install it with pip install Y": missing optional dependency errors — ImportError/ValueError raised when a library's optional extra was never installed — this error's family across 22 libraries.

Related errors

AI-assisted analysis of angular/angular-cli@bb72145f9a (2026-08-30). Data as JSON: /api/errors/f598ed099e8cd377. Report an issue: GitHub.