perf: avoid addComma when not necessary

index.js

@@ -369,12 +369,14 @@ function buildInnerObject (context, location) {
   code += 'let json = JSON_STR_BEGIN_OBJECT\n'
 
   let addComma = ''
-  if (!hasRequiredProperties) {
+  const hasComma = !hasRequiredProperties && (propertiesKeys.length > 1 || (schema.patternProperties || schema.additionalProperties !== false))
+  if (hasComma) {
     code += 'let addComma = false\n'
     addComma = '!addComma && (addComma = true) || (json += JSON_STR_COMMA)'
   }
 
-  for (const key of propertiesKeys) {
+  for (let i = 0; i < propertiesKeys.length; i++) {
+    const key = propertiesKeys[i]
     let propertyLocation = propertiesLocation.getPropertyLocation(key)
     if (propertyLocation.schema.$ref) {
       propertyLocation = resolveRef(context, propertyLocation)
@@ -387,14 +389,14 @@ function buildInnerObject (context, location) {
     code += `
       value = obj[${sanitizedKey}]
       if (value !== undefined) {
-        ${addComma}
+        ${i > 0 ? addComma : (hasComma ? 'addComma = true' : '')}
         json += ${JSON.stringify(sanitizedKey + ':')}
         ${buildValue(context, propertyLocation, 'value')}
       }`
 
     if (defaultValue !== undefined) {
       code += ` else {
-        ${addComma}
+        ${i > 0 ? addComma : (hasComma ? 'addComma = true' : '')}
         json += ${JSON.stringify(sanitizedKey + ':' + JSON.stringify(defaultValue))}
       }
       `

test/json-add-comma.test.js

@@ -0,0 +1,57 @@
+'use strict'
+
+const { test } = require('node:test')
+const build = require('..')
+
+test('additionalProperties: false', (t) => {
+  t.plan(1)
+  const stringify = build({
+    title: 'additionalProperties',
+    type: 'object',
+    properties: {
+      foo: {
+        type: 'string'
+      }
+    },
+    additionalProperties: false
+  })
+
+  const obj = { foo: 'a', bar: 'b', baz: 'c' }
+  t.assert.equal(stringify(obj), '{"foo":"a"}')
+})
+
+test('additionalProperties: {}', (t) => {
+  t.plan(1)
+  const stringify = build({
+    title: 'additionalProperties',
+    type: 'object',
+    properties: {
+      foo: {
+        type: 'string'
+      }
+    },
+    additionalProperties: {}
+  })
+
+  const obj = { foo: 'a', bar: 'b', baz: 'c' }
+  t.assert.equal(stringify(obj), '{"foo":"a","bar":"b","baz":"c"}')
+})
+
+test('additionalProperties: {type: string}', (t) => {
+  t.plan(1)
+  const stringify = build({
+    title: 'additionalProperties',
+    type: 'object',
+    properties: {
+      foo: {
+        type: 'string'
+      }
+    },
+    additionalProperties: {
+      type: 'string'
+    }
+  })
+
+  const obj = { foo: 'a', bar: 'b', baz: 'c' }
+  t.assert.equal(stringify(obj), '{"foo":"a","bar":"b","baz":"c"}')
+})