fix: anonymous callback handlers

.gitignore

@@ -1,3 +1,4 @@
 .DS_Store
 node_modules
 tmp
+dist

lib/index.js

@@ -25,11 +25,14 @@ const generateInside = ({ t, id, line, ch, timeout, extra } = {}) => {
     ),
     extra
       ? t.blockStatement([
-        t.expressionStatement(
-          t.callExpression(extra, [t.numericLiteral(line), t.numericLiteral(ch)])
-        ),
-        t.breakStatement(),
-      ])
+          t.expressionStatement(
+            t.callExpression(extra, [
+              t.numericLiteral(line),
+              t.numericLiteral(ch),
+            ])
+          ),
+          t.breakStatement(),
+        ])
       : t.breakStatement()
   );
 };
@@ -59,13 +62,17 @@ module.exports = (timeout = 100, extra = null) => {
   if (typeof extra === 'string') {
     const string = extra;
     extra = `() => console.error("${string.replace(/"/g, '\\"')}")`;
+  } else if (extra !== null) {
+    extra = extra.toString();
+    if (extra.startsWith('function (')) {
+      // fix anonymous functions as they'll cause
+      // the callback transform to blow up
+      extra = extra.replace(/^function \(/, 'function callback(');
+    }
   }
-  return ({ types: t, transform }) => {
-    const node = extra
-      ? transform(extra).ast.program.body[0]
-      : null;
 
-    // console.log(node && node.type)
+  return ({ types: t, transform }) => {
+    const node = extra ? transform(extra).ast.program.body[0] : null;
 
     let callback = null;
     if (t.isExpressionStatement(node)) {