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How to add and install dependencies?

Problem to Solve?

When creating schematics, you may encounter the need to install dependencies.

What does installing dependencies entail?

  1. Modifying the package.json file to include the new dependencies. Dependencies can be of various types: dev, default, peer, optional.
  2. Installing these dependencies based on the package.json file.


There are two main approaches to solving this problem:

  1. If you know the specific version of the library you want to install, you can directly modify the package.json and then run a task to install the dependencies.
  2. If you need to install the latest version but are unsure of its version number, you can call a Node method.


Adding Dependencies to the Package.json and Installing Them

The Angular Schematic repository provides useful utilities for this purpose.

import {
} from '@angular-devkit/schematics';
import {
} from '../../utils';
export function prettierFactory({packageManager}: { packageManager: string}): Rule {
return (tree: Tree, context: SchematicContext) => {
addPackageJsonDependency(tree, {
type: NodeDependencyType.Dev,
name: 'prettier',
version: '3.2.5',
overwrite: true,
return chain([
installDependencies(context, packageManager),
addScriptToPackageJson('format', 'prettier --write .')
export function installDependencies(context: SchematicContext, packageManager = 'npm') {
context.addTask(new NodePackageInstallTask({ packageManager }));
return noop();

Installing Dependencies with Node Commands

import {
} from '@angular-devkit/schematics';
import { Spinner } from '../../utils/spinner';
import { addScriptToPackageJson, spawnAsync } from '../../utils';
export function prettierFactory({packageManager}: { packageManager: string}): Rule {
return async () => {
const spinner = new Spinner('prettier installation');
const packageManagerCommands = {
npm: 'install',
yarn: 'add',
pnpm: 'add',
cnpm: 'install',
bun: 'add',
try {
spinner.start('Installing prettier');
await spawnAsync(
[ packageManagerCommands[packageManager], `--save-dev --save-exact prettier` ],
cwd: process.cwd(),
stdio: 'inherit',
shell: true,
spinner.succeed('Prettier was installed successfully');
} catch (e) {
return chain([
addScriptToPackageJson('format', 'prettier --write .')

Node Methods vs NodePackageInstallTask

We’ve explored two solutions. The first uses @angular-devkit’s native options, requiring more code. The second leverages Node.js’s spawnAsync, a native method.

The drawback of the second solution is its operation outside the staging area. This area allows the Tree object to roll back changes if any issues occur during modification of the package.json or any file. Additionally, the first solution supports dry-run mode, simulating actions without executing them. Thus, if you opt for the second solution, you’ll need to implement dry-run functionality manually.