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Building modules with Deno

Why Deno?

Writing and publishing modern JavaScript modules today can be painful. As a module author, your module should support CommonJS, ESM, and TypeScript declarations, as well as work in Deno, Node.js, and web browsers.

With Deno, writing your module is straightforward and can support all of the targets and formats needed to support the widest range of module users. The best part is that you can be productive immediately without needing to configure your toolchain or setup TypeScript.

dnt — Deno to Node transform

Once you have created your modern ES module, you can use dnt to transform your module into an npm module that: Supports CommonJS and ESM Runs test in both Deno and Node Supports TypeScript Works in both Deno, Node, and the browser

Here’s a sample dnt build script for a module called is-42:

import { build, emptyDir } from "https://deno.land/x/dnt@0.37.0/mod.ts";

await emptyDir("./npm");

await build({
  entryPoints: ["./mod.ts"],
  outDir: "./npm",
  shims: {
    deno: true,
  },
  package: {
    name: "is-42",
    version: Deno.args[0],
    description:
      "Boolean function that returns whether or not parameter is the number 42",
    license: "MIT",
    repository: {
      type: "git",
      url: "git+https://github.com/lambtron/is-42.git",
    },
    bugs: {
      url: "https://github.com/lambtron/is-42/issues",
    },
  },
  postBuild() {
    Deno.copyFileSync("LICENSE", "npm/LICENSE");
    Deno.copyFileSync("README.md", "npm/README.md");
  },
});

To run the build script:

$ deno run -A build_npm.ts 0.0.1

And its output:

[dnt] Transforming...
[dnt] Running npm install...

added 6 packages, and audited 7 packages in 2s

found 0 vulnerabilities
[dnt] Building project...
[dnt] Type checking ESM...
[dnt] Emitting ESM package...
[dnt] Emitting script package...
[dnt] Running post build action...
[dnt] Running tests...

> test
> node test_runner.js

Running tests in ./script/mod_test.js...

test 42 should return true ... ok
test 1 should return false ... ok

Running tests in ./esm/mod_test.js...

test 42 should return true ... ok
test 1 should return false ... ok
[dnt] Complete!

The CommonJS and ESM npm compatible packages are now in /npm, so publishing to npm requires only this step:

$ npm publish /npm
What about Node?
In Node, it’s common for module authors to write redundant code or complex build processes to ensure their package supports various formats and targets. Learn why Node.js and npm module resolution system is so complex and the problems it creates for developers.

Additional Resources

Here are some examples, blog posts, and videos about using Deno to create JavaScript modules.