npm:
specifiers
Since version 1.28, Deno has native support for importing npm packages. This is
done by importing using npm:
specifiers. For example the following code:
import { emojify } from "npm:node-emoji@2";
console.log(emojify(":t-rex: :heart: NPM"));
Can be run with:
$ deno run main.js
🦖 ❤️ NPM
When doing this, no npm install
is necessary and no node_modules
folder is
created. These packages are also subject to the same
permissions as other code in Deno.
npm specifiers have the following format:
npm:<package-name>[@<version-requirement>][/<sub-path>]
For examples with popular libraries, please refer to our tutorial section.
TypeScript types
Many packages ship with types out of the box, you can import those and use them with types easily:
import chalk from "npm:chalk@5";
Some packages do not though, but you can specify their types with a
@deno-types
directive. For example, using a
@types
package:
// @deno-types="npm:@types/express@^4.17"
import express from "npm:express@^4.17";
Module resolution
The official TypeScript compiler tsc
supports different
moduleResolution
settings. Deno only supports the modern node16
resolution. Unfortunately many
NPM packages fail to correctly provide types under node16 module resolution,
which can result in deno check
reporting type errors, that tsc
does not
report.
If a default export from an npm:
import appears to have a wrong type (with the
right type seemingly being available under the .default
property), it's most
likely that the package provides wrong types under node16 module resolution for
imports from ESM. You can verify this by checking if the error also occurs with
tsc --module node16
and "type": "module"
in package.json
or by consulting
the Are the types wrong? website
(particularly the "node16 from ESM" row).
If you want to use a package that doesn't support TypeScript's node16 module resolution, you can:
- Open an issue at the issue tracker of the package about the problem. (And perhaps contribute a fix :) (Although there unfortunately currently is a lack of tooling for packages to support both ESM and CJS, since default exports require different syntaxes, see also microsoft/TypeScript#54593)
- Use a CDN, that rebuilds the packages for Deno support, instead
of an
npm:
identifier. - Ignore the type errors you get in your code base with
// @ts-expect-error
or// @ts-ignore
.
Including Node types
Node ships with many built-in types like Buffer
that might be referenced in an
npm package's types. To load these you must add a types reference directive to
the @types/node
package:
/// <reference types="npm:@types/node" />
Note that it is fine to not specify a version for this in most cases because Deno will try to keep it in sync with its internal Node code, but you can always override the version used if necessary.
npm executable scripts
npm packages with bin
entries can be executed from the command line without an
npm install
using a specifier in the following format:
npm:<package-name>[@<version-requirement>][/<binary-name>]
For example:
$ deno run --allow-read npm:cowsay@1.5.0 Hello there!
______________
< Hello there! >
--------------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
$ deno run --allow-read npm:cowsay@1.5.0/cowthink What to eat?
______________
( What to eat? )
--------------
o ^__^
o (oo)\_______
(__)\ )\/\
||----w |
|| ||
--node-modules-dir
flag
npm specifiers resolve npm packages to a central global npm cache. This works
well in most cases and is ideal since it uses less space and doesn't require a
node_modules directory. That said, you may find cases where an npm package
expects itself to be executing from a node_modules
directory. To improve
compatibility and support those packages, you can use the --node-modules-dir
flag.
For example, given main.ts
:
import chalk from "npm:chalk@5";
console.log(chalk.green("Hello"));
Running this script with a --node-modules-dir
like so...
deno run --node-modules-dir main.ts
...will create a node_modules
folder in the current directory with a similar
folder structure to npm.
Note that this is all done automatically when calling deno run and there is no separate install command necessary.
Alternatively, if you wish to disable the creation of a node_modules
directory
entirely, you can set this flag to false (ex. --node-modules-dir=false
) or add
a "nodeModulesDir": false
entry to your deno.json configuration file to make
the setting apply to the entire directory tree.
In the case where you want to modify the contents of the node_modules
directory before execution, you can run deno cache
with --node-modules-dir
,
modify the contents, then run the script.
For example:
deno cache --node-modules-dir main.ts
deno run --allow-read=. --allow-write=. scripts/your_script_to_modify_node_modules_dir.ts
deno run --node-modules-dir main.ts