feat: Simple CSS injection support

src/cli-main.ts

@@ -84,7 +84,7 @@ export async function main(options: Options = {}) {
     })
     .option('--loader <ext=loader>', 'Specify the loader for a file extension')
     .option('--no-config', 'Disable config file')
-    .option('--no-shims', 'Disable cjs and esm shims')
+    .option('--inject-style', 'Inject style tag to document head')
     .action(async (files: string[], flags) => {
       const { build } = await import('.')
       Object.assign(options, {

src/esbuild/index.ts

@@ -109,7 +109,7 @@ export async function runEsbuild(
       }),
     options.tsconfigDecoratorMetadata && swcPlugin({ logger }),
     nativeNodeModulesPlugin(),
-    postcssPlugin({ css }),
+    postcssPlugin({ css, inject: options.injectStyle }),
     sveltePlugin({ css }),
     ...(options.esbuildPlugins || []),
   ]

src/esbuild/postcss.ts

@@ -1,12 +1,14 @@
 import fs from 'fs'
 import path from 'path'
-import { Plugin } from 'esbuild'
+import { Plugin, transform } from 'esbuild'
 import { getPostcss } from '../utils'
 
 export const postcssPlugin = ({
   css,
+  inject,
 }: {
   css?: Map<string, string>
+  inject?: boolean
 }): Plugin => {
   return {
     name: 'postcss',
@@ -25,7 +27,7 @@ export const postcssPlugin = ({
           const result = await loadConfig({}, path.dirname(file))
           configCache.set(file, result)
           return result
-        } catch (error) {
+        } catch (error: any) {
           if (error.message.includes('No PostCSS Config found in')) {
             const result = { plugins: [], options: {} }
             return result
@@ -34,45 +36,101 @@ export const postcssPlugin = ({
         }
       }
 
+      build.onResolve({ filter: /^#style-inject$/ }, () => {
+        return { path: '#style-inject', namespace: '#style-inject' }
+      })
+
+      build.onLoad(
+        { filter: /^#style-inject$/, namespace: '#style-inject' },
+        () => {
+          return {
+            // Taken from https://github.com/egoist/style-inject/blob/master/src/index.js (MIT)
+            contents: `
+          export default function styleInject(css, { insertAt } = {}) {
+            if (!css || typeof document === 'undefined') return
+
+            const head = document.head || document.getElementsByTagName('head')[0]
+            const style = document.createElement('style')
+            style.type = 'text/css'
+
+            if (insertAt === 'top') {
+              if (head.firstChild) {
+                head.insertBefore(style, head.firstChild)
+              } else {
+                head.appendChild(style)
+              }
+            } else {
+              head.appendChild(style)
+            }
+
+            if (style.styleSheet) {
+              style.styleSheet.cssText = css
+            } else {
+              style.appendChild(document.createTextNode(css))
+            }
+          }
+          `,
+            loader: 'js',
+          }
+        }
+      )
+
       build.onLoad({ filter: /\.css$/ }, async (args) => {
         let contents: string
 
         if (css && args.path.endsWith('.svelte.css')) {
-          contents = css.get(args.path) as string
+          contents = css.get(args.path)!
         } else {
           contents = await fs.promises.readFile(args.path, 'utf8')
         }
 
         // Load postcss config
         const { plugins, options } = await getPostcssConfig(args.path)
 
-        // Return if no postcss plugins are supplied
-        if (!plugins || plugins.length === 0) {
-          return {
-            contents,
-            loader: 'css',
+        if (plugins || plugins.length > 0) {
+          // Load postcss
+          const postcss = getPostcss()
+          if (!postcss) {
+            return {
+              errors: [
+                {
+                  text: `postcss is not installed`,
+                },
+              ],
+            }
           }
+
+          // Transform CSS
+          const result = await postcss
+            ?.default(plugins)
+            .process(contents, { ...options, from: args.path })
+
+          contents = result.css
         }
 
-        // Load postcss
-        const postcss = getPostcss()
-        if (!postcss) {
+        if (inject) {
+          contents = (
+            await transform(contents, {
+              minify: build.initialOptions.minify,
+              minifyIdentifiers: build.initialOptions.minifyIdentifiers,
+              minifySyntax: build.initialOptions.minifySyntax,
+              minifyWhitespace: build.initialOptions.minifyWhitespace,
+              loader: 'css',
+            })
+          ).code
+
+          contents = `import styleInject from '#style-inject';styleInject(${JSON.stringify(
+            contents
+          )})`
+
           return {
-            errors: [
-              {
-                text: `postcss is not installed`,
-              },
-            ],
+            contents,
+            loader: 'js',
           }
         }
 
-        // Transform CSS
-        const result = await postcss
-          ?.default(plugins)
-          .process(contents, { ...options, from: args.path })
-
         return {
-          contents: result.css,
+          contents,
           loader: 'css',
         }
       })

src/options.ts

@@ -123,8 +123,8 @@ export type Options = {
    */
   tsconfig?: string
   /**
-   * CJS and ESM shims
-   * @default `true`
+   * Inject CSS as style tags to document head
+   * @default {false}
    */
-  shims?: boolean
+  injectStyle?: boolean
 }

test/index.test.ts

@@ -697,3 +697,18 @@ test('decorator metadata', async (t) => {
   const contents = await getFileContent('dist/input.js')
   t.assert(contents.includes(`Reflect.metadata("design:type"`))
 })
+
+test('inject style', async (t) => {
+  const { outFiles, output } = await run(
+    t.title,
+    {
+      'input.ts': `import './style.css'`,
+      'style.css': `.hello { color: red }`
+    },
+    {
+      flags: ['--inject-style', '--minify'],
+    }
+  )
+  t.deepEqual(outFiles, ['input.js'])
+  t.assert(output.includes('.hello{color:red}'))
+})