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Replacement for 'npm link' that actually works. Allows to work on multiple packages locally at the same time.
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README.md

npm-local-development

Replacement for npm link done right for local development of multiple packages that are based on each other. It symlink root files using a watcher and excludes "peerDependencies", instead of using symlinks on the whole root. This makes it possible to really work locally on multiple packages that depend on each and have devDependencies checked out.

Install

npm i -g npm-local-development

How to use

You have basically two options:

1. Use lerna

If you have already a lerna.json you simply fire npm-local-development in the console in the same folder where your lerna.json is.

Example output (Lerna only):

$ npm-local-development --no-watcher
Read lerna.json ...
@deepkit/cli
  -> @deepkit/core
  -> @deepkit/core-node
@deepkit/core-node
  -> @deepkit/core
@deepkit/app
  -> @deepkit/core
@deepkit/electron
  -> @deepkit/core
  -> @deepkit/core-node
@deepkit/server
  -> @deepkit/core
  -> @deepkit/core-node
Ready

2. Use lerna + .links.json

You can additional to lerna possible create a new file .links.json and You enter all your links manually:

{
    "@shared/core": "../../my-library-repo/packages/core",
    "@shared/angular-button": "../../my-library-repo/packages/angular-button"
}

Example output (Lerna + .links.json):

$ npm-local-development --no-watcher
Read lerna.json ...
Read .links.json ...
@marcj/glut-client
  -> @marcj/glut-core
  -> @marcj/estdlib
  -> @marcj/marshal
@marcj/glut-integration
  -> @marcj/glut-client
  -> @marcj/glut-core
  -> @marcj/glut-server
  -> @marcj/estdlib
  -> @marcj/marshal
  -> @marcj/marshal-mongo
@marcj/glut-sample-angular
  -> @marcj/glut-client
  -> @marcj/glut-core
  -> @marcj/glut-server
  -> @marcj/marshal
  -> @marcj/marshal-mongo
@marcj/glut-server
  -> @marcj/glut-core
  -> @marcj/estdlib
  -> @marcj/estdlib-rxjs
  -> @marcj/marshal
  -> @marcj/marshal-mongo
@marcj/glut-core
  -> @marcj/estdlib-rxjs
  -> @marcj/marshal

3. Use arguments + .links.json

Given .links.json:

{
    "@shared/core": "../../my-library-repo/packages/core",
    "@shared/angular-button": "../../my-library-repo/packages/angular-button"
}

you need to define which actual root packages should link their dependencies to your links.json. So you can define those root packages as argument:

npm-local-development ./package-a ./package-b ...

NOTE: peerDependencies

Make sure that devDependencies that should not be synced (and thus the root package should use its own version) are in peerDependencies as well, otherwise your dependency will still use its own version of its dependencies.

Example:

If you have a @vendor/core package that has rxjs as devDependencies and that should be used by a root package, you need to put it (rxjs) also in peerDependencies (in @vendor/core), or @vendor/core will continue to use its own version of rxjs, which is not what you want.

You should not put rxjs in dependencies as this would always lead to non nominal instances. All instances of rxjs created by your @vendor/core package could not be detected as such using instanceof in the root package, as you end up having basically two version of rxjs.

NOTE: npm install

Note: When you want to use npm (npm install, npm uninstall, etc) please stop npm-local-development first. It reverts the structure back, so npm can continue to work.

NOTE: Symlinks

Note: You need to set env NODE_PRESERVE_SYMLINKS=1 to make this function. If you use TypeScript, set compilerOptions "preserveSymlinks": true.

NODE_PRESERVE_SYMLINKS=1 node_modules/.bin/ts-node --ignore='node_modules\/(?!@deepkit)' -- src/main.ts

Arguments

Use --no-watcher to run in one time only. Ideal for CI/build environments.

Working on multiple packages locally

When you work on 2 (or more) packages locally where one requires the other, you need to link them somehow, so you don't have to publish one and npm install in the other again and again. npm link was built to allow this, however npm link is fundamentally broken with modern architectures. See the section below "This tool solves multiples issues" to see why.

If those packages are directly related to each other, you usually should use Lerna to manage them all in one Git repository. It will make life way easier.

If that is not an option, you can use this tool nonetheless. Just go in each package and npm install as usual. If one package is completely new or not registered in npm registry, use

  "dependencies": {
    "@vendor/other-package": "file:../other-package"
  }

(Tip: @vendor is not necessary, but helps to keep things organised)

This creates automatically a link (node_modules/@vendor/other-package -> ../other-package) after running npm install.

Use now npm-local-development @vendor/other-package ../other-package in your root package folder. It removes the link and syncs now your dependencies correctly while your work on them.

Note: This tool does not npm install anything. Make sure you have all dependencies installed first. If you update dependencies, the tool restarts automatically.

If you have multiple such links, you should use create a .links.json config instead. See section "Working with more complex setup".

Working with Lerna

Usually, when you use Lerna, you work on multiple packages at the same time. E.g.

root
 | packages
 \__ core
 \__ frontend
 \__ server

When frontend and server requires the core package, Lerna symlinks them automatically, which leads to horrible errors that are not obvious at all. See the section below.

This tool can read your lerna.json and syncs the dependencies using a file watcher to solves all the issues below, so your build tools recognize the core as normal package like as it has been installed via npm directly.

Whenever you run lerna bootstrap, make sure to run npm-local-development as well.

It syncs now your dependencies correctly while your work on them.

TypeScript-only packages as dependency using ts-node

Per default ts-node disables compilation of node_modules. So when you have a core utils package that contains only TypeScript, you need to enable compiling for that.

package.json

  "scripts": {
    "run": "node_modules/.bin/ts-node --ignore 'node_modules/(?!@myName)' src/main.ts"
  }

I recommend to prefix your package names with your vendor name, so you have @myName/core, @myName/app, @myName/server etc.

If you use CLI tools like oclif which initialises ts-node on their own, use the environment variable:

bin/run

process.env['TS_NODE_IGNORE'] = 'node_modules/(?!@myName)';

require('@oclif/command').run()
.then(require('@oclif/command/flush'))
.catch(require('@oclif/errors/handle'));
....

bash:

TS_NODE_IGNORE='node_modules/(?!@myName)' my-binary

Angular 2+ TypeScript-only dependency

When working with Angular you need to include your packages in the compilation config:

tsconfig.json

  "include": [
    "node_modules/@myName/*/src/**/*.ts"
  ]

NOTE: Do not reference your packages relatively via import '../../@myName/core in your code, as this would break again the peerDependency resolution. Work with your local packages as if they have been installed via npm directly, then everything works fine.

Example:

import {coolFunction} from '@myName/core';

Create here an issue at Github https://github.com/marcj/npm-local-development/issues if you encounter problems.

This tool solves multiples issues

with local development of NPM packages that are tightly coupled to each other.

1. Symlinks break build tools and compiler like TypeScript & Angular

When you npm link a package outside of your build folder (where usually your tsconfig.json lies), TypeScript does not compile those files. You need to include those file in "includes": ["../other-package/**/*.ts"] manually. That's not a problem per se, as you could and should add those packages to includes either way. The problem arises when your other-package has peerDependencies, which you have installed in the root package: Node and the compiled won't find them, as it resolves the symlink first, and then the parent folder of other-package resolves to a different one. That resolved folder is usually not a children directory of your root package, so it can not find the actual packages in peerDependencies anymore. Also, symlinks forces you to install the peerDependencies in your other-package before you can use them correctly in the root package, but that leads to nominal types being broken, see point 2.

2. Nominal types break

When you npm link other-package while you're working on other-package, which means you have its devDependencies installed, those devDependencies overwrite your dependencies of the root package.

Example: If other-package uses RXJS as devDependencies and installed it (because you work on that package at the moment as well) you end up having 2 RXJS instances: One on your root node_modules/rxjs and one in node_modules/other-package/node_modules/rxjs.

Whenever you execute code in node_modules/other-package/utils.ts it will use its own RXJS code. You in the root package will use a different version of RXJS.

So, when your other-packages creates for example an Observable:

# other-package/index.ts

import {Observable} from 'rxjs';

export function promiseToObservable<T>(p: Promise<T>): Observable<T> {
    return new Observable((observer) => {
        p.then((v) => observer.next(v), (err) => observer.error(err));
    });
}

and you use it like

# main.js

import {Observable} from 'rxjs';
import {promiseToObservable} from 'other-package';

const myPromise = Promise.resolve();
const observable = promiseToObservable(myPromise);

observable instanceof Observable; // return false, which breaks stuff 

You see that observable is indeed a Observable instance, but not from your rxjs package, but from the one in node_modules/other-package/node_modules/rxjs, which leads to horrible errors that are not at all obvious. This tool fixes that - if (and only IF) you list rxjs in other-package's peerDependencies as you should (additionally to devDependencies so your IDE and test scripts still work).

3. Symlinks are not automatically synced in WebStorm

WebStorm does not resolve immediately changes made to the target behind symlinks and caches the "old" state. Using real files instead, the WebStorm IDE sees immediate changes.

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