mirror of
https://github.com/oven-sh/bun
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363 lines
9.1 KiB
Markdown
363 lines
9.1 KiB
Markdown
Bun provides a universal plugin API that can be used to extend both the _runtime_ and [_bundler_](/docs/bundler).
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Plugins intercept imports and perform custom loading logic: reading files, transpiling code, etc. They can be used to add support for additional file types, like `.scss` or `.yaml`. In the context of Bun's bundler, plugins can be used to implement framework-level features like CSS extraction, macros, and client-server code co-location.
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## Usage
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A plugin is defined as simple JavaScript object containing a `name` property and a `setup` function. Register a plugin with Bun using the `plugin` function.
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```tsx#myPlugin.ts
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import { plugin, type BunPlugin } from "bun";
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const myPlugin: BunPlugin = {
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name: "Custom loader",
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setup(build) {
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// implementation
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},
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};
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```
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Plugins have to be registered before any other code runs! To achieve this, use the `preload` option in your [`bunfig.toml`](/docs/runtime/bunfig). Bun automatically loads the files/modules specified in `preload` before running a file.
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```toml
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preload = ["./myPlugin.ts"]
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```
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To preload files before `bun test`:
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```toml
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[test]
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preload = ["./myPlugin.ts"]
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```
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## Third-party plugins
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By convention, third-party plugins intended for consumption should export a factory function that accepts some configuration and returns a plugin object.
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```ts
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import { plugin } from "bun";
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import fooPlugin from "bun-plugin-foo";
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plugin(
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fooPlugin({
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// configuration
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}),
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);
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```
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Bun's plugin API is loosely based on [esbuild](https://esbuild.github.io/plugins). Only [a subset](/docs/bundler/vs-esbuild#plugin-api) of the esbuild API is implemented, but some esbuild plugins "just work" in Bun, like the official [MDX loader](https://mdxjs.com/packages/esbuild/):
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```jsx
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import { plugin } from "bun";
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import mdx from "@mdx-js/esbuild";
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plugin(mdx());
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```
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## Loaders
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Plugins are primarily used to extend Bun with loaders for additional file types. Let's look at a simple plugin that implements a loader for `.yaml` files.
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```ts#yamlPlugin.ts
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import { plugin } from "bun";
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plugin({
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name: "YAML",
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async setup(build) {
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const { load } = await import("js-yaml");
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const { readFileSync } = await import("fs");
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// when a .yaml file is imported...
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build.onLoad({ filter: /\.(yaml|yml)$/ }, (args) => {
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// read and parse the file
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const text = readFileSync(args.path, "utf8");
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const exports = load(text) as Record<string, any>;
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// and returns it as a module
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return {
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exports,
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loader: "object", // special loader for JS objects
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};
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});
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},
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});
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```
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Register this file in `preload`:
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```toml#bunfig.toml
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preload = ["./yamlPlugin.ts"]
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```
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Once the plugin is registered, `.yaml` and `.yml` files can be directly imported.
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{% codetabs %}
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```ts#index.ts
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import data from "./data.yml"
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console.log(data);
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```
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```yaml#data.yml
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name: Fast X
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releaseYear: 2023
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```
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{% /codetabs %}
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Note that the returned object has a `loader` property. This tells Bun which of its internal loaders should be used to handle the result. Even though we're implementing a loader for `.yaml`, the result must still be understandable by one of Bun's built-in loaders. It's loaders all the way down.
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In this case we're using `"object"`—a built-in loader (intended for use by plugins) that converts a plain JavaScript object to an equivalent ES module. Any of Bun's built-in loaders are supported; these same loaders are used by Bun internally for handling files of various kinds. The table below is a quick reference; refer to [Bundler > Loaders](/docs/bundler/loaders) for complete documentation.
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{% table %}
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- Loader
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- Extensions
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- Output
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---
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- `js`
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- `.mjs` `.cjs`
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- Transpile to JavaScript files
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---
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- `jsx`
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- `.js` `.jsx`
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- Transform JSX then transpile
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---
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- `ts`
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- `.ts` `.mts` `.cts`
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- Transform TypeScript then transpile
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---
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- `tsx`
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- `.tsx`
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- Transform TypeScript, JSX, then transpile
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---
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- `toml`
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- `.toml`
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- Parse using Bun's built-in TOML parser
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---
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- `json`
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- `.json`
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- Parse using Bun's built-in JSON parser
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---
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- `napi`
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- `.node`
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- Import a native Node.js addon
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---
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- `wasm`
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- `.wasm`
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- Import a native Node.js addon
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---
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- `object`
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- _none_
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- A special loader intended for plugins that converts a plain JavaScript object to an equivalent ES module. Each key in the object corresponds to a named export.
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{% /callout %}
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Loading a YAML file is useful, but plugins support more than just data loading. Let's look at a plugin that lets Bun import `*.svelte` files.
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```ts#sveltePlugin.ts
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import { plugin } from "bun";
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plugin({
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name: "svelte loader",
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async setup(build) {
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const { compile } = await import("svelte/compiler");
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const { readFileSync } = await import("fs");
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// when a .svelte file is imported...
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build.onLoad({ filter: /\.svelte$/ }, ({ path }) => {
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// read and compile it with the Svelte compiler
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const file = readFileSync(path, "utf8");
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const contents = compile(file, {
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filename: path,
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generate: "ssr",
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}).js.code;
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// and return the compiled source code as "js"
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return {
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contents,
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loader: "js",
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};
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});
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},
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});
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```
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> Note: in a production implementation, you'd want to cache the compiled output and include additional error handling.
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The object returned from `build.onLoad` contains the compiled source code in `contents` and specifies `"js"` as its loader. That tells Bun to consider the returned `contents` to be a JavaScript module and transpile it using Bun's built-in `js` loader.
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With this plugin, Svelte components can now be directly imported and consumed.
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```js
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import "./sveltePlugin.ts";
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import MySvelteComponent from "./component.svelte";
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console.log(mySvelteComponent.render());
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```
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## Virtual Modules
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{% note %}
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This feature is currently only available at runtime with `Bun.plugin` and not yet supported in the bundler, but you can mimic the behavior using `onResolve` and `onLoad`.
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{% /note %}
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To create virtual modules at runtime, use `builder.module(specifier, callback)` in the `setup` function of a `Bun.plugin`.
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For example:
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```js
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import { plugin } from "bun";
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plugin({
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name: "my-virtual-module",
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setup(build) {
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build.module(
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// The specifier, which can be any string
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"my-transpiled-virtual-module",
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// The callback to run when the module is imported or required for the first time
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() => {
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return {
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contents: "console.log('hello world!')",
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loader: "js",
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};
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},
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);
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build.module("my-object-virtual-module", () => {
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return {
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exports: {
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foo: "bar",
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},
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loader: "object",
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};
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});
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},
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});
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// Sometime later
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// All of these work
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import "my-transpiled-virtual-module";
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require("my-transpiled-virtual-module");
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await import("my-transpiled-virtual-module");
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require.resolve("my-transpiled-virtual-module");
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import { foo } from "my-object-virtual-module";
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const object = require("my-object-virtual-module");
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await import("my-object-virtual-module");
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require.resolve("my-object-virtual-module");
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```
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### Overriding existing modules
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You can also override existing modules with `build.module`.
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```js
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import { plugin } from "bun";
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build.module("my-object-virtual-module", () => {
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return {
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exports: {
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foo: "bar",
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},
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loader: "object",
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};
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});
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require("my-object-virtual-module"); // { foo: "bar" }
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await import("my-object-virtual-module"); // { foo: "bar" }
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build.module("my-object-virtual-module", () => {
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return {
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exports: {
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baz: "quix",
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},
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loader: "object",
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};
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});
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require("my-object-virtual-module"); // { baz: "quix" }
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await import("my-object-virtual-module"); // { baz: "quix" }
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```
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## Reading the config
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Plugins can read and write to the [build config](/docs/bundler#api) with `build.config`.
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```ts
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Bun.build({
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entrypoints: ["./app.ts"],
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outdir: "./dist",
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sourcemap: "external",
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plugins: [
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{
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name: "demo",
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setup(build) {
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console.log(build.config.sourcemap); // "external"
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build.config.minify = true; // enable minification
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// `plugins` is readonly
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console.log(`Number of plugins: ${build.config.plugins.length}`);
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},
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},
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],
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});
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```
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## Reference
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```ts
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namespace Bun {
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function plugin(plugin: {
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name: string;
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setup: (build: PluginBuilder) => void;
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}): void;
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}
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type PluginBuilder = {
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onResolve: (
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args: { filter: RegExp; namespace?: string },
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callback: (args: { path: string; importer: string }) => {
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path: string;
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namespace?: string;
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} | void,
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) => void;
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onLoad: (
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args: { filter: RegExp; namespace?: string },
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callback: (args: { path: string }) => {
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loader?: Loader;
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contents?: string;
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exports?: Record<string, any>;
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},
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) => void;
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config: BuildConfig;
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};
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type Loader = "js" | "jsx" | "ts" | "tsx" | "json" | "toml" | "object";
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```
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The `onLoad` method optionally accepts a `namespace` in addition to the `filter` regex. This namespace will be be used to prefix the import in transpiled code; for instance, a loader with a `filter: /\.yaml$/` and `namespace: "yaml:"` will transform an import from `./myfile.yaml` into `yaml:./myfile.yaml`.
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