Excel Error Codes

Fix Excel Office Add-in Error: LRU Cache Is Not a Constructor

Chanuka Geekiyanage Sep 28, 2026 869 views

Question details

User is experiencing an 'LRU Cache is not a constructor' error during the npm start process for an Excel add-in.

Product: Microsoft Excel
Device & OS: not provided
Scenario: Developing or testing a custom Excel add-in created with the Yeoman generator after running a package update.
Observed behavior: The development server fails to start, throwing an error that states LRU Cache is not a constructor when running npm start.

Before you start

Ensure you have your exact error logs saved, note your current Node.js and npm versions, and document the specific packages that were recently updated before troubleshooting.

Solution 1Recommended

Troubleshoot Dependencies and Seek Developer Support

Attempt to resolve the node package conflicts locally, and if the issue persists, escalate it to the Microsoft Office development team.

This error is typically caused by a breaking change or version mismatch in the `lru-cache` npm package dependency within your Node.js environment. Resetting your packages or seeking official developer guidance is the best path forward.

Clean npm cache and reinstall dependencies

Open your terminal, delete your `node_modules` folder and `package-lock.json` file. Run `npm cache clean --force` followed by `npm install` to ensure a clean dependency installation.

Downgrade the problematic package

If the error persists, identify the version of `lru-cache` that was working previously. Update your `package.json` to lock this specific older version and run `npm install` again.

Gather project environment details

Document your Node.js version, operating system details, Yeoman generator version, and the complete error stack trace from your terminal.

Post to Microsoft Q&A

Visit the official Microsoft Q&A website and navigate to the Office Development section. Create a new question detailing your environment, reproduction steps, and error logs so the Office add-in development team can investigate the dependency change.

Troubleshoot Dependencies and Seek Developer Support

Community Support: The Microsoft Q&A Office Development tag is actively monitored by official Microsoft engineers who handle Yeoman generator and add-in bugs.

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Frequently Asked Questions

What causes the 'LRU Cache is not a constructor' error?

This error generally occurs when there is a mismatch or a breaking code change in the `lru-cache` npm package dependency, often triggered immediately after running a package update in a Node.js project.

How can I check my current npm package versions?

Open your command line interface in your project directory and run `npm list` to see a tree of all installed packages, or use `npm list lru-cache` to check the exact version causing the conflict.

Where is the best place to report Microsoft Office add-in bugs?

The official Microsoft Q&A platform under the 'Office Development' section is the recommended channel. Providing your Yeoman project details and error logs will help their team diagnose the issue quickly.

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Microsoft Office Error Codes