How to Fix NPM Package Not Working in Deno

Deno does not support npm packages directly because it uses ES modules and a different runtime. To fix this, use Deno's npm: specifier to import npm packages or find Deno-compatible versions. Also, ensure you run Deno with --unstable and --allow-net flags if needed.

Why This Happens

Deno is a modern runtime that uses ES modules and does not support Node.js-style CommonJS modules by default. Many npm packages are written for Node.js and rely on CommonJS or Node APIs, so importing them directly in Deno causes errors.

typescript

import express from "express";

console.log(express);

Output

error: Uncaught ImportError: Cannot find module "express"

The Fix

Use Deno's built-in npm support by prefixing the package name with npm: in your import statement. Run Deno with the --unstable flag to enable npm support. Also, add necessary permissions like --allow-net if the package needs network access.

typescript

import express from "npm:express";

console.log(typeof express);

Output

function

Prevention

Before using an npm package in Deno, check if it supports ES modules or if there is a Deno-specific version. Use Deno's deno.land/x third-party modules when possible. Always run Deno with --unstable when using npm packages and keep your Deno version updated.

Related Errors

Common related errors include:

• Cannot find module: Happens when the package is not installed or not imported with npm:.
• Module specifier must start with: Occurs if you forget the npm: prefix.
• Permission denied: Fix by adding appropriate --allow-* flags.

Key Takeaways

Deno requires the npm package import to use the npm: prefix and --unstable flag.

Many npm packages need Node.js APIs not available in Deno; check compatibility first.

Use Deno-specific modules from deno.land/x when possible for better support.

Always run Deno with necessary permissions like --allow-net for network packages.

Keep Deno updated to use the latest npm compatibility features.