All-in-one tooling

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In Node.js, before we can get started working on our project, we have to go through a configuration step for things like linting, formatting, and testing. Deno saves us a ton of time by including these tools natively. Let's take a look at what's included with these built-in CLI tools.

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Here we have a function called sing:

function sing(phrase: string, times: number): string {
  return Array(times).fill(phrase).join(" ");
}

Now let's run the formatter:

deno fmt

The formatter automatically formats your code to follow Deno's rules and conventions. Let's run it to clean up any formatting issues.

Deno even formats code snippets in markdown files. So anything that is enclosed in triple backticks will be formatted when you run this command as well.

The deno lint command is used to analyze your code for potential issues. It’s similar to ESLint but built into Deno.

deno lint --help

This will lint all of the JavaScript and TypeScript files in the current directory and in subdirectories.

You can also lint specific files by passing their names

# lint specific files
deno lint myfile1.ts myfile2.ts

You can run it on specific directories

deno lint src/

And if you're feeling like you want to skip linting certain files, at the top of the files, you can add a comment, and deno will know to skip this one.

// deno-lint-ignore-file
// deno-lint-ignore-file -- reason for ignoring

Deno also has some CLI commands for testing. In our directory here we have a test file. It uses the name of the function and test.

import { sing } from "./sing.ts";
import { assertEquals } from "jsr:@std/assert";

Deno.test("sing repeats a phrase", () => {
  const result = sing("La", 3);
  assertEquals(result, "La La La");
});

Now, we’ll run our tests using the deno test command. Deno automatically discovers and runs test files.

deno test

The way Deno decides which files should be considered test files is that it follows:

_test.ts, _test.js, _test.tsx, _test.jsx, .test.js, .test.ts, .test.tsx, .test.jsx

deno test encourage.test.js

Or you can pass a specific directory path and Deno will search for test files in there.

./tests/

You can even check code coverage. By default, when you run deno test --coverage a coverage profile will be generated in the /coverage directory in the current working directory.

deno test --coverage

From there you can run deno coverage to print a coverage report to standard output

deno coverage

As you can see, Deno's built-in tools are pretty cool. We don't have to spend a whole day configuring these settings before we can start working on our project. And we can format, lint, and test code without the need for third-party dependencies.