From 8fcd82922900f42d51ed1461926fe9f851091978 Mon Sep 17 00:00:00 2001
From: Ankit raj sharma <ankitrajsharma.125891@marwadiunivesity.ac.in>
Date: Tue, 29 Sep 2026 15:11:25 +0530
Subject: [PATCH 1/2] feat: support array and object (messageParams) input
 (#117)

---
 index.js           | 39 +++++++++++++++++++++++++++++++++++----
 test/index.test.js | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 4 deletions(-)

diff --git a/index.js b/index.js
index 4d8da8e..06af315 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,15 @@
 
 const { format } = require('node:util')
 
+const formatSpecifierRegex = /%[sdifjjoOc]/g
+
+function countFormatSpecifiers (str) {
+  if (typeof str !== 'string') return 0
+  const cleaned = str.replace(/%%/g, '')
+  const matches = cleaned.match(formatSpecifierRegex)
+  return matches ? matches.length : 0
+}
+
 function toString () {
   return `${this.name} [${this.code}]: ${this.message}`
 }
@@ -23,6 +32,8 @@ function createError (code, message, statusCode = 500, Base = Error, captureStac
 
   const FastifySpecificErrorSymbol = Symbol.for(`fastify-error ${code}`)
 
+  const expectedParams = countFormatSpecifiers(message)
+
   function FastifyError (...args) {
     if (!new.target) {
       return new FastifyError(...args)
@@ -32,12 +43,32 @@ function createError (code, message, statusCode = 500, Base = Error, captureStac
     this.name = 'FastifyError'
     this.statusCode = statusCode
 
-    const lastElement = args.length - 1
-    if (lastElement !== -1 && args[lastElement] && typeof args[lastElement] === 'object' && 'cause' in args[lastElement]) {
-      this.cause = args.pop().cause
+    let formatArgs = args
+    if (args.length === 1 && args[0] && typeof args[0] === 'object' && !(args[0] instanceof Error)) {
+      if ('messageParams' in args[0] || ('cause' in args[0] && expectedParams > 0)) {
+        if ('cause' in args[0]) {
+          this.cause = args[0].cause
+        }
+        if ('messageParams' in args[0]) {
+          formatArgs = Array.isArray(args[0].messageParams) ? args[0].messageParams : [args[0].messageParams]
+        } else if (expectedParams > 0) {
+          formatArgs = []
+        }
+      }
+    }
+
+    if (formatArgs === args) {
+      const lastElement = formatArgs.length - 1
+      if (lastElement !== -1 && formatArgs[lastElement] && typeof formatArgs[lastElement] === 'object' && 'cause' in formatArgs[lastElement]) {
+        this.cause = formatArgs.pop().cause
+      }
+
+      if (formatArgs.length === 1 && Array.isArray(formatArgs[0])) {
+        formatArgs = formatArgs[0]
+      }
     }
 
-    this.message = format(message, ...args)
+    this.message = format(message, ...formatArgs)
 
     Error.stackTraceLimit && captureStackTrace && Error.captureStackTrace(this, FastifyError)
   }
diff --git a/test/index.test.js b/test/index.test.js
index 3ad97f6..1a22508 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -230,3 +230,37 @@ test('check if FastifyError is instantiable', (t) => {
   t.assert.ok(err instanceof FastifyError)
   t.assert.ok(err instanceof Error)
 })
+
+test('Create error with array of parameters', (t) => {
+  t.plan(3)
+
+  const NewError = createError('CODE', 'hey %s, I like your %s')
+  const err = new NewError(['alice', 'attitude'])
+  t.assert.ok(err instanceof Error)
+  t.assert.equal(err.name, 'FastifyError')
+  t.assert.equal(err.message, 'hey alice, I like your attitude')
+})
+
+test('Create error with object input containing messageParams and cause', (t) => {
+  t.plan(4)
+
+  const cause = new Error('root cause')
+  const NewError = createError('CODE', 'hey %s, I like your %s')
+  const err = new NewError({ messageParams: ['alice', 'attitude'], cause })
+  t.assert.ok(err instanceof Error)
+  t.assert.equal(err.name, 'FastifyError')
+  t.assert.equal(err.message, 'hey alice, I like your attitude')
+  t.assert.equal(err.cause, cause)
+})
+
+test('Create error with object input containing only cause when format parameters exist', (t) => {
+  t.plan(3)
+
+  const cause = new Error('root cause')
+  const NewError = createError('CODE', 'hey %s')
+  const err = new NewError({ cause })
+  t.assert.ok(err instanceof Error)
+  t.assert.equal(err.message, 'hey %s')
+  t.assert.equal(err.cause, cause)
+})
+

From dc9a4842379fc4ab0bcecbce12cd020bcd28e1f2 Mon Sep 17 00:00:00 2001
From: Ankit raj sharma <ankitrajsharma666@gmail.com>
Date: Wed, 30 Sep 2026 15:56:58 +0530
Subject: [PATCH 2/2] fix(ci): fix linting trailing lines and achieve 100%
 branch coverage

Signed-off-by: Ankit raj sharma <ankitrajsharma666@gmail.com>
---
 index.js           | 1 -
 test/index.test.js | 9 +++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/index.js b/index.js
index 06af315..f674db6 100644
--- a/index.js
+++ b/index.js
@@ -5,7 +5,6 @@ const { format } = require('node:util')
 const formatSpecifierRegex = /%[sdifjjoOc]/g
 
 function countFormatSpecifiers (str) {
-  if (typeof str !== 'string') return 0
   const cleaned = str.replace(/%%/g, '')
   const matches = cleaned.match(formatSpecifierRegex)
   return matches ? matches.length : 0
diff --git a/test/index.test.js b/test/index.test.js
index 1a22508..ab79ac0 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -264,3 +264,12 @@ test('Create error with object input containing only cause when format parameter
   t.assert.equal(err.cause, cause)
 })
 
+test('Create error with object input containing single messageParams (non-array)', (t) => {
+  t.plan(3)
+
+  const NewError = createError('CODE', 'hey %s')
+  const err = new NewError({ messageParams: 'alice' })
+  t.assert.ok(err instanceof Error)
+  t.assert.equal(err.name, 'FastifyError')
+  t.assert.equal(err.message, 'hey alice')
+})