esbuild-svelte

Plugin to compile svelte components for bundling with esbuild.

Install

Install this plugin, esbuild and Svelte.

A simple build script looks like

import esbuild from "esbuild";
import sveltePlugin from "esbuild-svelte";

esbuild
  .build({
    entryPoints: ["app.js"],
    mainFields: ["svelte", "browser", "module", "main"],
    conditions: ["svelte", "browser"],
    bundle: true,
    outfile: "out.js",
    plugins: [sveltePlugin()],
    logLevel: "info",
  })
  .catch(() => process.exit(1));

The example-js folder of this repository is a great starting off point for a "complete" project. You can quickly get started using degit:

# Clone the JavaScript example to get started
npx degit EMH333/esbuild-svelte/example-js my-svelte-app

# Clone the TypeScript example to get started
npx degit EMH333/esbuild-svelte/example-ts my-svelte-app

CSS Output

By default, esbuild-svelte emits external css files from Svelte for esbuild to process. If this isn't desired, use a configuration that turns off external css output and instead includes it in the javascript output. For example: sveltePlugin({compilerOptions: {css: "injected"}})

Typescript and Other Svelte Preprocessing

In order to support Typescript and other languages that require preprocessing before being fed into the Svelte compiler, simply add the preprocessor to the preprocess option (which accepts both a single preprocessor or an array of them). The example script below is a great place to start, you can also look at the example-ts folder for a more complete project.

import esbuild from "esbuild";
import esbuildSvelte from "esbuild-svelte";
import sveltePreprocess from "svelte-preprocess";

esbuild
  .build({
    entryPoints: ["index.js"],
    mainFields: ["svelte", "browser", "module", "main"],
    conditions: ["svelte", "browser"],
    bundle: true,
    outdir: "./dist",
    plugins: [
      esbuildSvelte({
        preprocess: sveltePreprocess(),
      }),
    ],
  })
  .catch(() => process.exit(1));

Typescript in .svelte.ts files is supported natively.

svelte exports condition

If you are importing a svelte component library, you need to add "svelte" to conditions in esbuild build options. This lets esbuild use the svelte property in svelte component's exports conditions in package.json .

Advanced

For incremental or watch build modes, esbuild-svelte will automatically cache files if they haven't changed. This allows esbuild to skip the Svelte compiler for those files altogether, saving time. Setting cache: false will disable this file level cache if an issue arises (please report).

You can see the full API for this plugin here, which includes support for Svelte's compiler options, preprocessing API, and more.

Developing

Clone, npm install, npm link and it's good to go! Releases are automated (with the right permissions), just by running npm version patch|minor|major.