How to Fix Permission Denied Error in Deno

Deno runs with strict security by default and denies access to files, network, or environment without explicit permission. To fix permission denied errors, run your script with the appropriate permission flags like --allow-read or --allow-net to grant access.

Why This Happens

Deno is designed to be secure by default. It blocks access to your computer's files, network, or environment variables unless you explicitly allow it. This prevents accidental or malicious code from harming your system.

If you try to read a file or access the internet without permission, Deno will stop your program and show a permission denied error.

typescript

const data = await Deno.readTextFile("secret.txt");
console.log(data);

Output

error: Uncaught PermissionDenied: read access to "secret.txt" is not allowed
    at unwrapResponse (deno:core/core.js:226:13)
    at Object.sendSync (deno:core/core.js:232:10)
    at readTextFile (deno:runtime/js/40_files.js:34:10)
    at file:///app/script.ts:1:15

The Fix

To fix this error, you need to tell Deno to allow reading files by adding the --allow-read flag when running your script. This explicitly grants permission to read files.

For example, if your script reads a file, run it like this:

bash

deno run --allow-read script.ts

Output

Contents of secret.txt printed here (no error)

Prevention

Always run your Deno scripts with only the permissions they need. Avoid using --allow-all unless absolutely necessary, as it grants full access and reduces security.

Use specific flags like --allow-read, --allow-net, or --allow-env to limit permissions.

You can also use deno.json configuration files to manage permissions for larger projects.

Related Errors

Other permission errors you might see include:

• PermissionDenied: network access is not allowed - Fix by adding --allow-net flag.
• PermissionDenied: environment access is not allowed - Fix by adding --allow-env flag.
• PermissionDenied: write access is not allowed - Fix by adding --allow-write flag.

Key Takeaways

Deno blocks file, network, and environment access by default for security.

Use specific permission flags like --allow-read or --allow-net to fix permission denied errors.

Avoid using --allow-all to keep your code secure.

Manage permissions carefully in larger projects using deno.json configuration.

Related permission errors can be fixed by granting the correct access flags.