diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KarmaConfig.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KarmaConfig.kt
index a5304b39ab4..5040f021c83 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KarmaConfig.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KarmaConfig.kt
@@ -5,43 +5,33 @@
 
 package org.jetbrains.kotlin.gradle.targets.js.testing.karma
 
-// https://karma-runner.github.io/3.0/config/configuration-file.html
-class KarmaConfig {
-    var singleRun: Boolean = true
-    var autoWatch: Boolean = false
-    var basePath: String? = null
-    val files: MutableList<String> = mutableListOf()
-    val frameworks: MutableList<String> = mutableListOf()
-    val browsers: MutableList<String> = mutableListOf()
-    val customLaunchers: MutableMap<String, CustomLauncher> = mutableMapOf()
-    val reporters: MutableList<String> = mutableListOf()
-    val preprocessors: MutableMap<String, MutableList<String>> = mutableMapOf()
+// https://karma-runner.github.io/4.0/config/configuration-file.html
+data class KarmaConfig(
+    var singleRun: Boolean = true,
+    var autoWatch: Boolean = false,
+    var basePath: String? = null,
+    val files: MutableList<String> = mutableListOf(),
+    val frameworks: MutableList<String> = mutableListOf(),
+    val browsers: MutableList<String> = mutableListOf(),
+    val customLaunchers: MutableMap<String, CustomLauncher> = mutableMapOf(),
+    val reporters: MutableList<String> = mutableListOf(),
+    val preprocessors: MutableMap<String, MutableList<String>> = mutableMapOf(),
     var coverageReporter: CoverageReporter? = null
+) {
+    data class CoverageReporter(
+        var dir: String,
+        val reporters: MutableList<Reporter> = mutableListOf()
+    ) {
 
-    class CoverageReporter(var dir: String) {
-        val reporters = mutableListOf<Reporter>()
-
-        class Reporter(
+        data class Reporter(
             val type: String,
             val subDir: String? = null,
             val file: String? = null
-        ) {
-            override fun toString(): String {
-                return "Reporter(type='$type', subDir=$subDir, file=$file)"
-            }
-        }
-
-        override fun toString(): String {
-            return "CoverageReporter(dir='$dir', reporters=$reporters)"
-        }
+        )
     }
 
     class CustomLauncher(var base: String) {
         val flags = mutableListOf<String>()
         var debug: Boolean? = null
     }
-
-    override fun toString(): String {
-        return "KarmaConfig(singleRun=$singleRun, autoWatch=$autoWatch, basePath=$basePath, files=$files, frameworks=$frameworks, browsers=$browsers, reporters=$reporters, preprocessors=$preprocessors, coverageReporter=$coverageReporter)"
-    }
 }
\ No newline at end of file