diff --git a/build/lib/spawn.js b/build/lib/spawn.js
new file mode 100644
index 00000000..e0483a5d
--- /dev/null
+++ b/build/lib/spawn.js
@@ -0,0 +1,16 @@
+import { spawn } from 'child_process';
+
+const spawns = new Set();
+
+export function spawnAndCheck(cmd, args, options) {
+  const s = spawn(cmd, args, options);
+  spawns.add(s);
+  s.on('close', (code) => {
+    spawns.delete(s);
+    if (code !== 0) {
+      console.error(cmd, 'exited with code:', code);
+      [...spawns].forEach((s) => s.kill());
+      process.exit(code);
+    }
+  });
+}
diff --git a/build/tools/build.js b/build/tools/build.js
index 2996824e..a8cd4813 100644
--- a/build/tools/build.js
+++ b/build/tools/build.js
@@ -1,14 +1,14 @@
-import { spawn } from 'child_process';
 import { mkdirSync } from 'fs';
+import { spawnAndCheck } from '../lib/spawn.js';
 
 mkdirSync('out', { recursive: true });
 
-spawn('node', ['build/tools/copy.js'], {
+spawnAndCheck('node', ['build/tools/copy.js'], {
   shell: true,
   stdio: 'inherit',
 });
 
-spawn('./node_modules/.bin/rollup', ['-c'], {
+spawnAndCheck('./node_modules/.bin/rollup', ['-c'], {
   shell: true,
   stdio: 'inherit',
 });
diff --git a/build/tools/serve.js b/build/tools/serve.js
index 0e7d1a53..1db73bee 100644
--- a/build/tools/serve.js
+++ b/build/tools/serve.js
@@ -1,23 +1,8 @@
-import { spawn } from 'child_process';
 import { mkdirSync } from 'fs';
+import { spawnAndCheck } from '../lib/spawn.js';
 
 mkdirSync('out', { recursive: true });
 
-const spawns = new Set();
-
-function spawnAndCheck(cmd, args, options) {
-  const s = spawn(cmd, args, options);
-  spawns.add(s);
-  s.on('close', (code) => {
-    spawns.delete(s);
-    if (code !== 0) {
-      console.error(cmd, 'exited with code:', code);
-      [...spawns].forEach((s) => s.kill());
-      process.exit(code);
-    }
-  });
-}
-
 spawnAndCheck('npm', ['run', 'watch'], {
   shell: true,
   stdio: 'inherit',