January 11, 2023

Understanding the anatomy of package-lock.json

Making sure the proper dependencies and versions are installed one package at a time


Package-lock.json is a file that is automatically generated by the package manager npm (short for Node Package Manager) when you install packages in your project. It serves as a lock file that ensures that the packages and their dependencies are installed in a specific and consistent manner, even if the versions of the packages are updated in the future.

Why do I need to understand it?

Understanding the anatomy of package-lock.json can be helpful for a number of reasons. For example, if you are working on a project with a team and you need to ensure that everyone has the same versions of the packages installed, you can use package-lock.json to do so.

Additionally, if you are having issues with your project and you think they may be related to the packages you have installed, package-lock.json can provide valuable information about the specific versions of the packages that are being used.

So, what does package-lock.json look like and what information does it contain?

At the top level, package-lock.json is a JSON file that contains an object with several properties. The most important property is "dependencies", which is an object that contains all of the packages that have been installed in the project, along with their dependencies.

For each package, package-lock.json lists the specific version that is being used, as well as the dependencies of that package. For example, if you have installed the package Lodash in your project, package-lock.json might contain the following information:

In this example, we can see that the package Lodash is being used in version 4.17.15 and that it has a dependency on the package lodash.debounce, which is version 4.0.8 or higher.

In addition to the dependencies property, package-lock.json also contains the name and version properties, which specify the name and version of the project, respectively. It also contains a lockfileVersion property, which specifies the version of the package-lock.json file format being used.

There are also several other properties that can be present in package-lock.json, depending on the specific packages and their dependencies that are being used in the project. For example, the requires property lists the packages that are required by the project, and the devDependencies property lists the packages that are only needed for development purposes (e.g. testing, building, etc.).

It's important to note that package-lock.json should not be edited manually. If you need to update the packages or their dependencies in your project, you should use the package manager (e.g. npm) to do so, and it will update package-lock.json accordingly. This ensures that the lock file remains accurate and correct.


At its most simplistic definition, package-lock.json makes sure we install the correct packages and their dependencies. If you want to learn more, check out the official npm documentation of package-lock.json. Thanks for reading!