CODEWITHSUNDEEP
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Reputation: 1067

How to add dev-only dependencies in Deno?

In Node.js, we can use npm install -D foo to add a dependency into package.json > devDependencies. When the package is published and used as a dependency, devDependencies won't be installed.

But in deno.json, there is only imports, no devImports. According to Deno v2 RC announcement, we can use deno add --dev. But this only add contents to deno.lock, not adding anything to deno.json. I tried deno add --dev eslint (not migrating Deno Lint yet), but it complained eslint: command not found.

When package.json exists, it's added to package.json, but I'm trying finding a pure-Deno solution.

I found denoland/deno#26865, but no answers are there.

Upvotes: 4

Views: 676

Answers (1)

rsenna
rsenna

Reputation: 11973

See this answer by "crowKats" here, but in short:

With a “npm-style” Deno project, based on package.json, use

  • deno add --dev for dev dependencies, or
  • deno add for production dependencies.

But with a deno.json or deno.jsonc project, use

  • deno add, in either case.

There’s no need to segregate development and production dependencies for Deno 2+ native projects. Deno is smart: it only caches and installs the dependencies needed for the current runtime.

While I’m not a Deno expert myself (still learning), my suggestion is that you need to read Deno's documentation attentively but also with an "open mind" (don't expect it to just be a cuter, giant-lizard version of npm):

  • In the npm world, npm install is required before running any project, otherwise the application will break: dependencies wont't be available in node_modules when some code tries to access it.

  • With Deno-style though, there is no node_modules, and dependencies might also be cached automatically at runtime. You can (and should, especially in production) run deno cache ahead of time, of course. But if you, say, add a new dependency or make a hotfix change in production, Deno's expected behaviour is to detect it, automatically download the dependency to its cache, and continue executing the application without further interruption.

  • To make things even weirder, this also means not even deno add is totally required. According to Deno's docs, imports in the code should be "unequivocal": e.g. they must specify the package registry or source - with the npm:, node: or jsr: prefixes, for example. And this "extra" info is enough for Deno's runtime to repopulate its cache, if needed.

References:

Upvotes: 1

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