perf(serializer): avoid addComma when not necessary

index.js

@@ -372,12 +372,14 @@ function buildInnerObject (context, location) {
   code += 'let json = JSON_STR_BEGIN_OBJECT\n'
 
   let addComma = ''
-  if (!hasRequiredProperties) {
+  const needComma = !hasRequiredProperties && (propertiesKeys.size > 1 || (schema.patternProperties || schema.additionalProperties !== false))
+  if (needComma) {
     code += 'let addComma = false\n'
     addComma = '!addComma && (addComma = true) || (json += JSON_STR_COMMA)'
   }
 
   let counterValue = 0
+  let i = 0
   for (const key of propertiesKeys) {
     let propertyLocation = propertiesLocation.getPropertyLocation(key)
     if (propertyLocation.schema.$ref) {
@@ -399,7 +401,7 @@ function buildInnerObject (context, location) {
 
     if (defaultValue !== undefined) {
       code += ` else {
-        ${addComma}
+        ${i > 0 ? addComma : (needComma ? 'addComma = true' : '')}
         json += ${JSON.stringify(sanitizedKey + ':' + JSON.stringify(defaultValue))}
       }
       `
@@ -415,6 +417,8 @@ function buildInnerObject (context, location) {
     if (hasRequiredProperties) {
       addComma = 'json += \',\''
     }
+
+    i++
   }
 
   if (schema.patternProperties || schema.additionalProperties) {
@@ -587,10 +591,10 @@ function buildArray (context, location) {
       functionCode += `
         if (${i} < arrayLength) {
           if (${buildArrayTypeCondition(item.type, value)}) {
-            ${tmpRes}
-            if (${i} < arrayEnd) {
+            if (${i}) {
               json += JSON_STR_COMMA
             }
+            ${tmpRes}
           } else {
             throw new Error(\`Item at ${i} does not match schema definition.\`)
           }
@@ -601,21 +605,21 @@ function buildArray (context, location) {
     if (schema.additionalItems) {
       functionCode += `
         for (let i = ${itemsSchema.length}; i < arrayLength; i++) {
-          json += JSON.stringify(obj[i])
-          if (i < arrayEnd) {
+          if (i) {
             json += JSON_STR_COMMA
           }
+          json += JSON.stringify(obj[i])
         }`
     }
   } else {
     const code = buildValue(context, itemsLocation, 'value')
     functionCode += `
       for (let i = 0; i < arrayLength; i++) {
-        const value = obj[i]
-        ${code}
-        if (i < arrayEnd) {
+        if (i) {
           json += JSON_STR_COMMA
         }
+        const value = obj[i]
+        ${code}
       }`
   }
 

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"}')
+})