Node module import map

Generate importmap for node_modules.

Presentation

This repository generates import map from package.json files in your node_modules directory. The generated importmap can be used to make code dependent of node module executable in a browser.

See code relying on node module resolution

import lodash from "lodash"

The code above is expecting Node.js to "magically" find file corresponding to "lodash". This magic is the node esm resolution algorithm. Other runtimes than Node.js, a browser like Chrome for instance, don't have this algorithm. Executing that code in a browser fetches http://example.com/lodash and likely results in 404 File Not Found from server.

Usage

1 - Install @jsenv/node-module-import-map

npm install --save-dev @jsenv/node-module-import-map

2 - Create generate-import-map.js

import { getImportMapFromProjectFiles, writeImportMapFile } from "@jsenv/node-module-import-map"

const projectDirectoryUrl = new URL("./", import.meta.url)

await writeImportMapFile(
  [
    getImportMapFromProjectFiles({
      projectDirectoryUrl,
    }),
  ],
  {
    projectDirectoryUrl,
    importMapFileRelativeUrl: "./project.importmap",
  },
)

The code above is written in ESM. You may have to use .mjs extension to run it with Node.js as documented in enabling ESM

3 - Generate project.importmap

node generate-import-map.js

4 - Add project.importmap to your html

<!DOCTYPE html>
<html>
  <head>
    <title>Title</title>
    <meta charset="utf-8" />
    <link rel="icon" href="data:," />
    <script type="importmap" src="./project.importmap"></script>
  </head>

  <body>
    <script type="module">
      import lodash from "lodash"
    </script>
  </body>
</html>

If you use a bundler or an other tool, be sure it's compatible with import maps. As import map are standard the bundler/tool might be compatible by default or with the help of some plugin/configuration. @jsenv/core seamlessly supports importmap during development, testing and when building for production.

API

writeImportMapFile

writeImportMapFile is an async function receiving an array of promise resolving to importmaps. It awaits for every importmap, compose them into one and write it into a file.

writeImportMapFile code example

Code below generate an import map from node_modules + an inline importmap.

import { getImportMapFromProjectFiles, writeImportMapFile } from "@jsenv/node-module-import-map"

const projectDirectoryUrl = new URL("./", import.meta.url)
const importMapInputs = [
  getImportMapFromProjectFiles({
    projectDirectoryUrl,
    dev: true,
  }),
  {
    imports: {
      foo: "./bar.js",
    },
  },
]

await writeImportMapFile(importMapInputs, {
  projectDirectoryUrl,
  importMapFileRelativeUrl: "./import-map.importmap",
})

implementation

importMapInputs parameter

importMapInputs is an array of importmap object or promise resolving to importmap objects. This parameter is optional and is an empty array by default.

When importMapInputs is empty a warning is emitted and writeImportMapFile write an empty importmap file.

importMapFile parameter

importMapFile parameter is a boolean controling if importMap is written to a file. This parameters is optional and enabled by default.

importMapFileRelativeUrl parameter

importMapFileRelativeUrl parameter is a string controlling where importMap file is written. This parameter is optional and by default it's "./import-map.importmap".

getImportMapFromProjectFiles

getImportMapFromProjectFiles is an async function returning an importMap object computed from infos found in package.json files and source files.

The following source of information are used to create complete and coherent mappings in the importmap.

Your package.json
All dependencies declared in package.json are searched into node_modules, recursively.
In every package.json, "main", "exports" and "imports" field.
All static and dynamic import found in files, recursively.

getImportMapFromProjectFiles code example

import { getImportMapFromProjectFiles } from "@jsenv/node-module-import-map"

const importMap = await getImportMapFromProjectFiles({
  projectDirectoryUrl: new URL("./", import.meta.url),
  dev: false,
  runtime: "browser",
})

Be sure node modules are on your filesystem because we'll use the filesystem structure to generate the importmap. For that reason, you must use it after npm install or anything that is responsible to generate the node_modules folder and its content on your filesystem.

implementation

projectDirectoryUrl parameter

projectDirectoryUrl parameter is a string url leading to a folder with a package.json. This parameters is required and accepted values are documented in @jsenv/util#assertAndNormalizeDirectoryUrl

dev parameter

dev parameter is a boolean indicating if the importmap will be used for development or production. This parameter is optional and by default it's disabled.

When enabled the following happens:

devDependencies declared in your package.json are included in the generated importMap.
"development" is favored over "production" in package.json conditions

runtime parameter

runtime parameter is a string indicating where the importmap will be used. This parameter is optional with a default of "browser".

When runtime is "browser", "browser" is favored over "node" in package.json conditions.

When it is "node", "node" is favored.

treeshakeMappings parameter

treeshakeMappings parameter is a boolean controlling if mappings will be treeshaked according to the import found in your files.

When enabled, only the mappings actually used by your files will be generated. It will drastically decrease the importmap file size. This is the default behaviour as long as dev parameter is disabled.

When disabled, all mappings needed for node esm module resolution will be generated. During development, you can start/stop using a mapping at any time. In that case it's more convenient to keep unused mappings in the generated importmap. Consequently treeshakeMappings parameter is disabled when dev parameter is enabled.

initialImportMap parameter

initialImportMap parameter is an importMap object. This parameter is optional and by default it's an empty object.

You can use this parameter to provide mappings that are not already in your package.json.

import { getImportMapFromProjectFiles } from "@jsenv/node-module-import-map"

const importMap = await getImportMapFromProjectFiles({
  projectDirectoryUrl: new URL("./", import.meta.url),
  initialImportMap: {
    imports: {
      foo: "./bar.js",
    },
  },
})

console.log(importMap.imports.foo) // "./bar.js"

getImportMapFromFile

getImportMapFromFile is an async function reading importmap from a file.

getImportMapFromFile code example

import { getImportMapFromFile } from "@jsenv/node-module-import-map"

const importMap = await getImportMapFromFile({
  projectDirectoryUrl: new URL("./", import.meta.url),
  importMapRelativeUrl: "./import-map.importmap",
})

implementation

importMapFileRelativeUrl

importMapFileRelativeUrl parameter is an url relative to projectDirectoryUrl leading to the importmap file. This parameter is required.

Custom node module resolution

@jsenv/node-module-import-map uses a custom node module resolution

It behaves as Node.js with one big change:

A node module will not be found if it is outside your project directory.

We do this because import map are used on the web where a file outside project directory cannot be reached.

In practice, it has no impact because node modules are inside your project directory. If they are not, ensure all your dependencies are in your package.json and re-run npm install.

Extensionless import

If the code you wants to run contains one ore more extensionless path specifier, it will not be found by a browser (not even by Node.js).

extensionless import example

import { foo } from "./file"

In this situation, you can do one of the following:

Add extension in the source file
If there is a build step, ensure extension are added during the build

Add remapping in exports field of your package.json

{
  "exports": {
    "./file": "./file.js"
  }
}

Or using Subpath patterns

{
  "exports": {
    "./*": "./*.js"
  }
}

Remap manually each extensionless import and pass that importmap in initialImportMap

Configure VSCode and ESLint for importmap

VSCode and ESLint can be configured to understand importmap. This will make ESLint and VSCode capable to resolve your imports. Amongst other things it will give you the following:

ESLint tells your when an import file cannot be found (help to fix typo)
ESLint tells your when a named import does not exists in an imported file (help to fix typo too)
VSCode "go to definition" opens the imported file (cmd + click too)
VSCode autocompletion is improved because it can read imported files

The animated image below shows how configuring ESLint and VSCode helps to fix an import with a typo and navigate to an imported file. This example uses "demo/log.js" import that is remapped to "src/log.js" by docs/vscode-importmap-demo/custom.importmap

To configure VSCode, pass jsConfigFile: true to writeImportMapFile. When jsConfigFile parameter is enabled, writeImportMapFile convert mappings into paths into a file called jsconfig.json. This file is used by VSCode to resolve imports.

jsConfigFile code example

import { writeImportMapFile } from "@jsenv/node-module-import-map"

await writeImportMapFile(
  [
    {
      imports: {
        "src/": "./src/",
      },
    },
  ],
  {
    projectDirectoryUrl: new URL("./", import.meta.url),
    jsConfigFile: true,
  },
)

Code above would result into the following jsconfig.json file

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "src/*": ["./src/*"]
    }
  }
}

At this stage, VSCode is configured to understand import mappings. It means "Go to definition" is working and allow you to navigate in your codebase using cmd+click keyboard shortcut.

If you also want to configure ESLint to resolve import using importmap, follow steps described in @jsenv/importmap-eslint-resolver

@jsenv/node-module-import-map

Node module import map

Presentation

Usage

API

writeImportMapFile

getImportMapFromProjectFiles

getImportMapFromFile

Custom node module resolution

Extensionless import

Configure VSCode and ESLint for importmap

Readme

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@jsenv/node-module-import-map

Node module import map

Presentation

Usage

API

writeImportMapFile

getImportMapFromProjectFiles

getImportMapFromFile

Custom node module resolution

Extensionless import

Configure VSCode and ESLint for importmap

Readme

Keywords

Package Sidebar

Install

Repository

Homepage

DownloadsWeekly Downloads

Version

License

Unpacked Size

Total Files

Last publish

Collaborators

Weekly Downloads