feat: support esbuild config

README.md

@@ -283,6 +283,7 @@ export default {
       sourceRewriteMatch: "",
       firebaseJson: "",
       cloudRunBuildDir: "",
+      esbuildBuildOptions: (defaultOptions: BuildOptions) => Promise<BuildOptions> | BuildOptions,
     }),
     target: "#svelte",
   },
@@ -459,6 +460,47 @@ export default {
 
 </details>
 
+<details>
+<summary><code>esbuildBuildOptions</code></summary>
+
+As an escape hatch, you may optionally specify a function which will receive the final esbuild options generated by this adapter and returns a modified esbuild configuration. The result of this function will be passed as-is to esbuild. The function can be async.
+
+For example, you may wish to add a plugin:
+
+```js
+import firebase from "svelte-adapter-firebase";
+
+/** @type {import('@sveltejs/kit').Config} */
+export default {
+  kit: {
+    adapter: firebase({
+      esbuildBuildOptions(defaultOptions) {
+        return {
+          ...defaultOptions,
+          plugins: []
+        }
+      }
+    }),
+    target: "#svelte",
+  },
+};
+```
+
+The default options for this version are as follows:
+
+```js
+{
+	entryPoints: ['.svelte-kit/firebase/handler.js'],
+	outfile: `pathToOutputDir/index.js`,
+	bundle: true,
+	inject: ['pathTo/shims.js'],
+	platform: 'node'
+}
+```
+
+</details>
+
+
 ## Cloud Function
 
 With this `firebase.json` and `functions/` dir in a standard SvelteKit app structure and default `svelte-adapter-firebase` config:

package.json

@@ -44,14 +44,14 @@
   "devDependencies": {
     "@commitlint/cli": "^11.0.0",
     "@commitlint/config-conventional": "^11.0.0",
-    "@sveltejs/kit": "^1.0.0-next.110",
+    "@sveltejs/kit": "1.0.0-next.132",
     "@types/express": "^4.17.12",
     "@types/node": "^14.14.35",
     "ava": "^3.15.0",
     "firebase-functions": "^3.14.1",
     "husky": "^5.0.8",
     "typescript": "^4.2.3",
-    "xo": "^0.40.1"
+    "xo": "^0.40.3"
   },
   "scripts": {
     "prepare": "husky install",