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Exploring the Deno Permissions Module A Comprehensive Guide

By David Li on 2024-03-05T01:45:04.000Z

Exploring the Deno Permissions Module: A Comprehensive Guide

Deno, a secure runtime for JavaScript and TypeScript, has gained significant traction in the development community since its initial release. One of the most appealing aspects of Deno is its focus on security, which is evident in its Permissions module. This article provides an in-depth look at the Deno Permissions module, explaining its purpose, usage, and best practices.

Why Permissions Matter in Deno

Deno was designed to improve security in comparison to its predecessor, Node.js. By default, Deno scripts cannot access the file system, network, or environment variables without explicit permission. This is a major leap forward in preventing unauthorized access to sensitive data or system resources.

In Deno, permissions are granted through flags passed to the script runner. The Permissions module serves as an interface to query and revoke permissions during the script execution.

Getting Started with the Deno Permissions Module

To use the Deno Permissions module, you’ll need to import it from the Deno standard library:

import { Permissions } from "https://deno.land/std@0.115.0/permissions/mod.ts";

Note: Make sure to replace the version number with the latest available version from the Deno standard library.

Querying Permissions

Before using sensitive resources in your code, it’s a good practice to check if the required permissions have been granted. You can query permissions using the query() method:

const netPermissionStatus = await Permissions.query({ name: "net" });

if (netPermissionStatus.state === "granted") {
  // Use the network resource
} else {
  console.error("Network permission is required to continue.");

The query() method accepts an object describing the permission you want to check. The returned object contains a state property, indicating the permission state as either “granted”, “denied”, or “prompt”.

Requesting Permissions

In some cases, you may want to request permissions from the user during runtime. You can achieve this using the request() method:

const envPermissionStatus = await Permissions.request({ name: "env" });

if (envPermissionStatus.state === "granted") {
  // Access environment variables
} else {
  console.error("Environment permission is required to continue.");

The request() method works similarly to query(), but it will prompt the user for permission if the permission state is “prompt”. If the permission is already granted or denied, it will return the current state without prompting the user.

Revoking Permissions

To further enhance security, you can revoke permissions using the revoke() method:

const writePermissionStatus = await Permissions.revoke({ name: "write" });

if (writePermissionStatus.state === "granted") {
  console.error("Write permission should have been revoked.");
} else {
  console.log("Write permission successfully revoked.");

Revoking permissions may be useful when you no longer need access to a resource, or when you want to restrict access after performing a sensitive operation.


The Deno Permissions module offers an essential interface for managing permissions in your applications. By leveraging this module, you can enhance the security and user trust of your applications. Remember to always query or request permissions before accessing sensitive resources, and consider revoking them when they are no longer needed.

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