packages/server: Return API errors as JSON

packages/server/src/middleware/ErrorApiHandler.ts

@@ -11,7 +11,7 @@ export class ErrorApiHandler implements IMiddleware {
       req.correlationId, err.stack)
     const statusCode = this.getStatus(err)
     res.status(statusCode)
-    if (err instanceof ValidationError) {
+    if (ValidationError.isInstanceOf(err)) {
       res.json({
         error: err.message,
         errors: err.errors,

packages/server/src/validator/ValidationError.ts

@@ -15,4 +15,10 @@ export class ValidationError extends Error {
     this.name = 'ValidationError'
     Error.captureStackTrace(this)
   }
+
+  static isInstanceOf(err: any): err is ValidationError {
+    return typeof err.status === 'number'
+      && typeof err.message === 'string'
+      && Array.isArray(err.errors)
+  }
 }