If you have been around JavaScript projects for a while, you have probably used both npm install and npm ci without thinking too much about it. They seem to do the same thing: install dependencies. But under the hood, they behave quite differently – and that difference matters, especially in CI/CD pipelines.
Let’s break it down in plain terms.
Think of it like packing for a trip
Imagine you’re packing a suitcase.
- npm install is like packing based on a list you wrote a while ago. You might tweak things a bit, swap items, or grab newer versions if available.
- npm ci is like using a strict checklist someone already finalized. You follow it exactly – no changes, no surprises.
What 'npm install' really does
When you run ‘npm install’, npm looks at your package.json and installs dependencies based on version ranges (like ^1.2.0).
That means:
- it might install slightly newer versions than last time
- it updates your package-lock.json if needed
- it’s flexible, which is great during development
In short: it tries to make things work, even if that means adjusting versions.
What 'npm ci' really does
Now compare that with ‘npm ci’
This command is much stricter:
- it only uses package-lock.json
- it installs exactly the versions listed there
- it fails immediately if something doesn’t match
- it deletes node_modules before installing
In short: it ensures everything is exactly the same every time.
The impact in test automation
If you are running automated tests (especially in CI/CD), consistency is everything.
You don’t want a test to pass today and fail tomorrow just because a minor dependency version changed.
When to use what
Use npm install when:
- you’re developing locally
- adding or updating dependencies
- you don’t mind small version changes
Use npm ci when:
- running tests in CI pipelines
- you need reproducible builds
- stability matters more than flexibility