From the npm-link documentation:

In the local module directory:

$ cd ./package-dir
$ npm link

In the directory of the project to use the module:

$ cd ./project-dir
$ npm link package-name

Or in one go using relative paths:

$ cd ./project-dir
$ npm link ../package-dir

This is equivalent to using two commands above under the hood.

Since asked and answered by the same person, I'll add a npm link as an alternative.

from docs:

This is handy for installing your own stuff, so that you can work on it and test it iteratively without having to continually rebuild.

cd ~/projects/node-bloggy  # go into the dir of your main project
npm link ../node-redis     # link the dir of your dependency

[Edit] As of NPM 2.0, you can declare local dependencies in package.json

"dependencies": {
    "bar": "file:../foo/bar"
  }

npm pack + package.json

This is what worked for me:

STEP 1: In module project, execute npm pack:

This will build a <package-name>-<version>.tar.gz file.

STEP 2: Move the file to the consumer project

Ideally you can put all such files in a tmp folder in your consumer-project root:

STEP 3: Refer it in your package.json:

"dependencies": {
  "my-package": "file:/./tmp/my-package-1.3.3.tar.gz"
}

STEP 4: Install the packages:

npm install or npm i or yarn

Now, your package would be available in your consumer-project's node_modules folder.

Good Luck...

Neither of these approaches (npm link or package.json file dependency) work if the local module has peer dependencies that you only want to install in your project's scope.

For example:

/local/mymodule/package.json

"name": "mymodule",
"peerDependencies":
{
  "foo": "^2.5"
}

/dev/myproject/package.json

"dependencies":
{
  "mymodule": "file:/local/mymodule",
  "foo": "^2.5"
}

In this scenario, npm sets up myproject's node_modules/ like this:

/dev/myproject/node_modules/
 ↳ foo/
 ↳ mymodule -> /local/mymodule

When node loads mymodule and it does require('foo'), node resolves the mymodule symlink, and then only looks in /local/mymodule/node_modules/ (and its ancestors) for foo, which it doen't find. Instead, we want node to look in /local/myproject/node_modules/, since that's where were running our project from, and where foo is installed.

So, we either need a way to tell node to not resolve this symlink when looking for foo, or we need a way to tell npm to install a copy of mymodule when the file dependency syntax is used in package.json. I haven't found a way to do either, unfortunately :(

So I had a lot of problems with all of the solutions mentioned so far...

I have a local package that I want to always reference (rather than npm link) because it won't be used outside of this project (for now) and also won't be uploaded to an npm repository for wide use as of yet.

I also need it to work on Windows AND Unix, so sym-links aren't ideal.

Pointing to the tar.gz result of (npm package) works for the dependent npm package folder, however this causes issues with the npm cache if you want to update the package. It doesn't always pull in the new one from the referenced npm package when you update it, even if you blow away node_modules and re-do your npm-install for your main project.

so.. This is what worked well for me!

Main Project's Package.json File Snippet:

  "name": "main-project-name",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    ...
    "preinstall": "cd ../some-npm-package-angular && npm install && npm run build"
  },
  "private": true,
  "dependencies": {
    ...
    "@com/some-npm-package-angular": "file:../some-npm-package-angular/dist",
    ...
  }

This achieves 3 things:

• Avoids the common error (at least with angular npm projects) "index.ts is not part of the compilation." - as it points to the built (dist) folder.
• Adds a preinstall step to build the referenced npm client package to make sure the dist folder of our dependent package is built.
• Avoids issues where referencing a tar.gz file locally may be cached by npm and not updated in the main project without lots of cleaning/troubleshooting/re-building/re-installing.

I hope this is clear, and helps someone out.

The tar.gz approach also sort of works..

npm install (file path) also sort of works.

This was all based off of a generated client from an openapi spec that we wanted to keep in a separate location (rather than using copy-pasta for individual files)

====== UPDATE: ======

There are additional errors with a regular development flow with the above solution, as npm's versioning scheme with local files is absolutely terrible. If your dependent package changes frequently, this whole scheme breaks because npm will cache your last version of the project and then blow up when the SHA hash doesn't match anymore with what was saved in your package-lock.json file, among other issues.

As a result, I recommend using the *.tgz approach with a version update for each change. This works by doing three things.

First:

For your dependent package, use the npm library "ng-packagr". This is automatically added to auto-generated client packages created by the angular-typescript code generator for OpenAPI 3.0.

As a result the project that I'm referencing has a "scripts" section within package.json that looks like this:

  "scripts": {
    "build": "ng-packagr -p ng-package.json",
    "package": "npm install && npm run build && cd dist && npm pack"
  },

And the project referencing this other project adds a pre-install step to make sure the dependent project is up to date and rebuilt before building itself:

  "scripts": {
    "preinstall": "npm run clean && cd ../some-npm-package-angular && npm run package"
  },

Second

Reference the built tgz npm package from your main project!

  "dependencies": {
    "@com/some-npm-package-angular": "file:../some-npm-package-angular/dist/some-npm-package-angular-<packageVersion>.tgz",
    ...
  }

Third

Update the dependent package's version EVERY TIME you update the dependent package. You'll also have to update the version in the main project.

If you do not do this, NPM will choke and use a cached version and explode when the SHA hash doesn't match. NPM versions file-based packages based on the filename changing. It won't check the package itself for an updated version in package.json, and the NPM team stated that they will not fix this, but people keep raising the issue: https://github.com/microsoft/WSL/issues/348

for now, just update the:

"version": "1.0.0-build5",

In the dependent package's package.json file, then update your reference to it in the main project to reference the new filename, ex:

"dependencies": {
       "@com/some-npm-package-angular": "file:../some-npm-package-angular/dist/some-npm-package-angular-1.0.0-build5.tgz",
        ...
}

You get used to it. Just update the two package.json files - version then the ref to the new filename.

Hope that helps someone...

Missing the main property?

As previous people have answered npm i --save ../location-of-your-packages-root-directory. The ../location-of-your-packages-root-directory however must have two things in order for it to work.

1. package.json in that directory pointed towards

2. main property in the package.json must be set and working i.g. "main": "src/index.js", if the entry file for ../location-of-your-packages-root-directory is ../location-of-your-packages-root-directory/src/index.js

I came across different solution than above while installing custom build package for CKEditor5.

So I uploaded package to app root directory, than:

npm add file:./ckeditor5

In my package.json package is listed as a file:

"ckeditor5-custom-build": "file:ckeditor5",

I think this answer could be relevant to the topic on how to add local package.

As explained in the accepted answer by @fancy, you can use this command:

npm install ...<path_to_your_local_package>

to add your local packages.

In the package.json of your project it will create an entry like:

"dependencies": {
    ...
    "your_package_name": "file:...<path_to_your_local_package>"
    ...
}

If the package you're including is within the project root, then it will do an installation of all the dependencies of your included local package. Otherwise, i.e. if it's outside your project root, it will simply create a symbolic link (as @frank-tan pointed out), in which case, if for some reason you've deleted the node_modules directory in your project or you need to do a fresh reinstall you must run:

npm install --install-links

The command line option install-links ensures that all dependencies of the local packages get installed automatically. This will come in handy if, for example, you're using Jenkins and need to deploy a large project with many custom-developed nested dependencies.

See official npm-install documentation for more detail: https://docs.npmjs.com/cli/v9/commands/npm-install

For installing local module / package, that not yet on npm or you are developing an npm package and want to test it locally before publishing it. You can try this -

npm i yalc -g

Go to the module/package folder then -

yalc publish

Your packakge is ready to use, now go the project you want to install it -

yalc add <Your package name>

Package will be installed to you project. If you want to remove it -

yalc remove <Your package name>

Keep It Simple!

You can use lnk-cli to create a directory link.

Here’s my setup using TypeScript:

• common (Contains all .ts files I want to share)
• server (This is a BullBoard server)
• functions (This is a Firebase project)

Step 1: Install lnk-cli

• Install globally, see here.

Step 2: Common Folder

Only include the code files you want (no package.json, tsconfig.json, etc.)

Step 3: Package.json

See the highlighted text. Just add the "lnk" command to create the directory link before watching the TypeScript files.

Step 4: .gitignore

The common folder has the main code, so you can ignore these linked folders. Any changes in one of the three locations (common, functions/common, or server/common) will automatically reflect in all linked locations.

Done!

Now you can import the common files like this. (No additional need to adjust tsconfig.json)

For more recent versions of npm (I'm using 8.1.3 under macOS Big Sur), the sequence of commands is even easier...

cd /path-where-your-local-project-is/
npm init

This will ask you for some data related to your project and properly initialises your project.json file.

Once that is done, you can install additional modules with:

cd /path-where-your-local-project-is/
npm install --save-dev some-npm-module .

That's all you need!

Note: I believe that the trailing dot is not necessary if you're inside the project directory, but I also think that it doesn't hurt to add it :-)

(I wonder why the official docs still don't explain this...)