add onExtract option

README.md

@@ -238,6 +238,12 @@ Type: `id => void`
 
 A function to be invoked when an import for CSS file is detected.
 
+### onExtract
+
+Type: `({ code, map, codeFilePath, mapFilePath }) => any`
+
+A function to be invoked before extracting CSS file, you can make it return `false` to disable CSS extraction.
+
 ## License
 
 MIT © [EGOIST](https://github.com/egoist)

src/index.js

@@ -132,14 +132,26 @@ export default (options = {}) => {
         code += `\n/*# sourceMappingURL=${basename}.css.map */`
       }
 
+      // Release for potential next build
+      extracted = []
+
+      if (options.onExtract) {
+        const shouldExtract = await options.onExtract({
+          code,
+          map: concat.sourceMap,
+          codeFilePath: file,
+          mapFilePath: file + '.map'
+        })
+        if (shouldExtract === false) {
+          return
+        }
+      }
+
       await Promise.all([
         fs.writeFile(file, code, 'utf8'),
         sourceMap === true &&
           fs.writeFile(file + '.map', concat.sourceMap, 'utf8')
       ])
-
-      // Release for potential next build
-      extracted = []
     }
   }
 }

test/__snapshots__/index.test.js.snap

@@ -322,6 +322,13 @@ console.log(style$1);
 "
 `;
 
+exports[`onExtract 1`] = `
+"'use strict';
+
+console.log(undefined, undefined);
+"
+`;
+
 exports[`postcss-config: js code 1`] = `
 "'use strict';
 

test/index.test.js

@@ -239,3 +239,18 @@ snapshot({
     inject: false
   }
 })
+
+test('onExtract', async () => {
+  const res = await write({
+    input: 'simple/index.js',
+    dirname: 'onExtract',
+    options: {
+      extract: true,
+      onExtract() {
+        return false
+      }
+    }
+  })
+  expect(await res.jsCode()).toMatchSnapshot()
+  expect(await res.hasCssFile()).toBe(false)
+})