> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Invalidate Cache

> This guide explores how GitHub Actions invalidates and rebuilds the NPM cache when project dependencies change.

In this guide, we’ll explore how GitHub Actions invalidates and rebuilds the NPM cache when your project’s dependencies change. You’ll learn how cache keys work, how to trigger a cache rebuild, and how to verify the new cache in your repository.

## Background

GitHub Actions uses cache keys to store and restore dependencies. By hashing `package-lock.json`, we ensure that any update to dependencies generates a new cache key, invalidating the old cache automatically.

Key points:

* We cache `node_modules` using the hash of `package-lock.json`.
* Changing dependencies updates the lock file, resulting in a new cache key.
* A new cache is created when the key doesn’t match any existing cache.

## Local Setup

First, clone the repository and switch to the feature branch:

```bash theme={null}
git clone <repo-url>
cd solar-system
git checkout feature/exploring-workflow
git pull
```

Open `package.json` to review current dependencies:

```json theme={null}
{
  "name": "Solar_System",
  "version": "6.6.7",
  "author": "Siddharth Barahalikar <barahalikar.siddharth@gmail.com>",
  "homepage": "https://www.linkedin.com/in/barahalikar-siddharth/",
  "license": "MIT",
  "scripts": {
    "start": "node app.js",
    "test": "mocha app-test.js --timeout 10000 --reporter mocha-junit-reporter --exit",
    "coverage": "nyc --reporter cobertura --reporter lcov --reporter text --reporter json-summary mocha app-test.js --timeout 10000"
  },
  "nyc": {
    "check-coverage": true,
    "lines": 90
  },
  "dependencies": {
    "cors": "^2.8.5",
    "express": "^4.18.2",
    "mocha-junit-reporter": "2.2.1",
    "mongoose": "5.13.20",
    "nyc": "^15.1.0"
  },
  "devDependencies": {
    "chai": "*",
    "chai_http": "*",
    "mocha": "*"
  }
}
```

## Adding a New Dependency

Let’s simulate a dependency change by installing `nodemon`:

```bash theme={null}
npm install nodemon --save
```

Your `package.json` will now include:

```json theme={null}
"dependencies": {
  "cors": "^2.8.5",
  "express": "^4.18.2",
  "mocha-junit-reporter": "2.2.1",
  "mongoose": "5.13.20",
  "nyc": "^15.1.0",
  "nodemon": "3.0.1"
}
```

Commit and push the changes:

```bash theme={null}
git add package.json package-lock.json
git commit -m "Add nodemon dependency"
git push
```

## Workflow Cache Configuration

Our GitHub Actions workflow uses the official `actions/cache` action to save and restore `node_modules`:

```yaml theme={null}
- name: Cache NPM dependencies
  uses: actions/cache@v3
  with:
    path: node_modules
    key: ${{ runner.os }}-node-modules-${{ hashFiles('package-lock.json') }}
```

| Field  | Description                                            |
| ------ | ------------------------------------------------------ |
| `path` | Directory to cache (`node_modules`)                    |
| `key`  | Cache key including OS and hash of `package-lock.json` |
| `uses` | Action version (`actions/cache@v3`)                    |

When you push a change to `package-lock.json`, the `hashFiles` function produces a new key, and the workflow cannot find an existing cache that matches it.

## Observing the Workflow

After pushing your commit, the workflow runs again. In the **Unit Testing** job, open the **Cache NPM dependencies** step:

<Frame>
  ![The image shows a GitHub Actions workflow page for a repository named "solar-system," displaying the progress of unit testing and code coverage jobs. The workflow is currently in progress with some jobs completed.](https://kodekloud.com/kk-media/image/upload/v1752876500/notes-assets/images/GitHub-Actions-Invalidate-Cache/github-actions-solar-system-workflow.jpg)
</Frame>

You’ll see:

> **No cache was found**

<Frame>
  ![The image shows a GitHub Actions workflow interface for a project named "solar-system," displaying the status of unit testing jobs on different environments, with a focus on caching NPM dependencies.](https://kodekloud.com/kk-media/image/upload/v1752876501/notes-assets/images/GitHub-Actions-Invalidate-Cache/github-actions-solar-system-workflow-2.jpg)
</Frame>

The runner installs dependencies afresh and then uploads the new cache. Since parallel jobs may try to save the same cache simultaneously:

<Callout icon="lightbulb" color="#1CB2FE">
  If multiple jobs use the same cache key, one job will succeed in saving while the others may report a save failure. This is expected behavior.
</Callout>

Finally, verify the new cache in your repository’s **Caches** section:

<Frame>
  ![The image shows a GitHub Actions interface displaying cache details for a project, including cache keys, sizes, and last used times.](https://kodekloud.com/kk-media/image/upload/v1752876502/notes-assets/images/GitHub-Actions-Invalidate-Cache/github-actions-cache-details-interface.jpg)
</Frame>

## Summary

* GitHub Actions invalidates caches when the cache key changes.
* Hashing `package-lock.json` ensures dependencies are up to date.
* You can confirm the cache status in the workflow logs and the **Caches** tab.

## Links and References

* [actions/cache – GitHub Docs](https://docs.github.com/actions/advanced-guides/caching-dependencies-to-speed-up-workflows)
* [npm cache documentation](https://docs.npmjs.com/cli/v9/commands/npm-cache)

<CardGroup>
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