How to Use node: Specifier in Deno for Node.js Compatibility

In Deno, you can use the node: specifier to import Node.js built-in modules directly, like import fs from "node:fs". This allows you to write code compatible with Node.js APIs while running in Deno. Make sure to enable the --unstable flag and have the --compat mode enabled if needed.

Syntax

The node: specifier is used as a prefix in import statements to load Node.js built-in modules in Deno. It tells Deno to resolve the module as a Node.js core module.

• import <name> from "node:<module>"; - imports the Node.js built-in module named <module>.
• <name> - the variable name you assign the imported module to.
• <module> - the Node.js core module name, like fs, path, or crypto.

This syntax is similar to Node.js ES module imports but works in Deno with compatibility enabled.

typescript

import fs from "node:fs";
import path from "node:path";

console.log(typeof fs.readFileSync); // function
console.log(typeof path.join); // function

Example

This example shows how to import the Node.js fs and path modules using the node: specifier in Deno. It reads the current file's content and prints the file name using path.basename.

typescript

import fs from "node:fs";
import path from "node:path";

const filePath = new URL(import.meta.url).pathname;
const content = fs.readFileSync(filePath, "utf-8");
const fileName = path.basename(filePath);

console.log(`File name: ${fileName}`);
console.log(`Content length: ${content.length}`);

Output

File name: example.ts
Content length: 200

Common Pitfalls

Common mistakes when using the node: specifier in Deno include:

• Not running Deno with the --unstable flag, which is required for Node.js compatibility features.
• Forgetting to enable --compat mode to allow Node.js built-in modules to work properly.
• Using Node.js modules that rely on native binaries or APIs not supported by Deno's compatibility layer.
• Trying to import Node.js modules without the node: prefix, which will fail in Deno.

Example of wrong and right import:

typescript

/* Wrong: Missing node: prefix */
// import fs from "fs"; // This will fail in Deno

/* Right: Using node: prefix */
import fs from "node:fs";
console.log(typeof fs.readFileSync); // function

Output

function

Quick Reference

Usage	Description
import mod from "node:";	Import Node.js built-in module in Deno
--unstable flag	Required to enable Node.js compatibility features
--compat flag	Enables Node.js compatibility mode in Deno
Use node: prefix	Must prefix Node.js core modules with node:
Not all modules supported	Some Node.js modules may not work due to native dependencies

Key Takeaways

Use the node: prefix to import Node.js built-in modules in Deno.

Run Deno with --unstable and --compat flags to enable Node.js compatibility.

Not all Node.js modules work in Deno due to native or unsupported APIs.

Always use import statements like import fs from "node:fs"; in Deno for Node.js modules.

Check Deno documentation for the latest support and compatibility details.