diff --git a/tools/cli/src/main/java/org/teavm/cli/devserver/TeaVMDevServerRunner.java b/tools/cli/src/main/java/org/teavm/cli/devserver/TeaVMDevServerRunner.java
index ff75518ea..0750ffdb5 100644
--- a/tools/cli/src/main/java/org/teavm/cli/devserver/TeaVMDevServerRunner.java
+++ b/tools/cli/src/main/java/org/teavm/cli/devserver/TeaVMDevServerRunner.java
@@ -30,6 +30,7 @@ import org.apache.commons.cli.Option;
 import org.apache.commons.cli.Options;
 import org.apache.commons.cli.ParseException;
 import org.eclipse.jetty.util.log.Log;
+import org.teavm.backend.javascript.JSModuleType;
 import org.teavm.common.json.JsonParser;
 import org.teavm.devserver.DevServer;
 import org.teavm.tooling.ConsoleTeaVMToolLog;
@@ -80,6 +81,12 @@ public final class TeaVMDevServerRunner {
                 .hasArgs()
                 .longOpt("property")
                 .build());
+        options.addOption(Option.builder()
+                .argName("module_type")
+                .hasArg()
+                .longOpt("js-module-type")
+                .desc("JS module type (umd, common-js, es2015 or none)")
+                .build());
         options.addOption(Option.builder()
                 .argName("number")
                 .hasArg()
@@ -182,6 +189,18 @@ public final class TeaVMDevServerRunner {
         if (commandLine.hasOption("preserved-classes")) {
             devServer.getPreservedClasses().addAll(List.of(commandLine.getOptionValues("preserved-classes")));
         }
+        if (commandLine.hasOption("js-module-type")) {
+            var moduleTypeValue = commandLine.getOptionValue("js-module-type");
+            JSModuleType type;
+            try {
+                type = JSModuleType.valueOf(moduleTypeValue.toUpperCase().replace('-', '_'));
+            } catch (IllegalArgumentException e) {
+                System.err.println("Invalid value for --js-module-type: " + moduleTypeValue);
+                printUsage();
+                type = null;
+            }
+            devServer.setJsModuleType(type);
+        }
 
         if (commandLine.hasOption("proxy-url")) {
             devServer.setProxyUrl(commandLine.getOptionValue("proxy-url"));
diff --git a/tools/devserver/src/main/java/org/teavm/devserver/CodeServlet.java b/tools/devserver/src/main/java/org/teavm/devserver/CodeServlet.java
index 88e8e0583..cd68e3bf3 100644
--- a/tools/devserver/src/main/java/org/teavm/devserver/CodeServlet.java
+++ b/tools/devserver/src/main/java/org/teavm/devserver/CodeServlet.java
@@ -67,6 +67,7 @@ import org.eclipse.jetty.websocket.client.ClientUpgradeRequest;
 import org.eclipse.jetty.websocket.client.WebSocketClient;
 import org.eclipse.jetty.websocket.client.io.UpgradeListener;
 import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
+import org.teavm.backend.javascript.JSModuleType;
 import org.teavm.backend.javascript.JavaScriptTarget;
 import org.teavm.cache.InMemoryMethodNodeCache;
 import org.teavm.cache.InMemoryProgramCache;
@@ -122,6 +123,7 @@ public class CodeServlet extends HttpServlet {
     private String proxyBaseUrl;
     private Map<String, String> properties = new LinkedHashMap<>();
     private List<String> preservedClasses = new ArrayList<>();
+    private JSModuleType jsModuleType;
 
     private Map<String, Supplier<InputStream>> sourceFileCache = new HashMap<>();
 
@@ -223,6 +225,10 @@ public class CodeServlet extends HttpServlet {
         return properties;
     }
 
+    public void setJsModuleType(JSModuleType jsModuleType) {
+        this.jsModuleType = jsModuleType;
+    }
+
     public void setLogBuildErrors(boolean logBuildErrors) {
         this.logBuildErrors = logBuildErrors;
     }
@@ -882,6 +888,9 @@ public class CodeServlet extends HttpServlet {
         jsTarget.setObfuscated(false);
         jsTarget.setAstCache(astCache);
         jsTarget.setDebugEmitter(debugInformationBuilder);
+        if (jsModuleType != null) {
+            jsTarget.setModuleType(jsModuleType);
+        }
         jsTarget.setStrict(true);
         vm.setOptimizationLevel(TeaVMOptimizationLevel.SIMPLE);
         vm.setCacheStatus(classSource);
diff --git a/tools/devserver/src/main/java/org/teavm/devserver/DevServer.java b/tools/devserver/src/main/java/org/teavm/devserver/DevServer.java
index 5537252e8..66725be12 100644
--- a/tools/devserver/src/main/java/org/teavm/devserver/DevServer.java
+++ b/tools/devserver/src/main/java/org/teavm/devserver/DevServer.java
@@ -23,6 +23,7 @@ import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.server.ServerConnector;
 import org.eclipse.jetty.servlet.ServletContextHandler;
 import org.eclipse.jetty.servlet.ServletHolder;
+import org.teavm.backend.javascript.JSModuleType;
 import org.teavm.tooling.TeaVMToolLog;
 
 public class DevServer {
@@ -40,6 +41,7 @@ public class DevServer {
     private List<DevServerListener> listeners = new ArrayList<>();
     private Map<String, String> properties = new LinkedHashMap<>();
     private List<String> preservedClasses = new ArrayList<>();
+    private JSModuleType jsModuleType;
     private boolean compileOnStartup;
     private boolean logBuildErrors = true;
 
@@ -123,6 +125,10 @@ public class DevServer {
         return properties;
     }
 
+    public void setJsModuleType(JSModuleType jsModuleType) {
+        this.jsModuleType = jsModuleType;
+    }
+
     public void invalidateCache() {
         servlet.invalidateCache();
     }
@@ -170,6 +176,7 @@ public class DevServer {
         servlet.setLogBuildErrors(logBuildErrors);
         servlet.getProperties().putAll(properties);
         servlet.getPreservedClasses().addAll(preservedClasses);
+        servlet.setJsModuleType(jsModuleType);
         for (DevServerListener listener : listeners) {
             servlet.addListener(listener);
         }
diff --git a/tools/gradle/src/main/java/org/teavm/gradle/TeaVMPlugin.java b/tools/gradle/src/main/java/org/teavm/gradle/TeaVMPlugin.java
index 819ffbe02..fcb8afa06 100644
--- a/tools/gradle/src/main/java/org/teavm/gradle/TeaVMPlugin.java
+++ b/tools/gradle/src/main/java/org/teavm/gradle/TeaVMPlugin.java
@@ -147,6 +147,7 @@ public class TeaVMPlugin implements Plugin<Project> {
             task.getMainClass().convention(js.getMainClass());
             task.getClasspath().from(task.getProject().getConfigurations().getByName(CLASSPATH_CONFIGURATION_NAME));
             task.getPreservedClasses().addAll(js.getPreservedClasses());
+            task.getJsModuleType().convention(js.getModuleType());
             task.getProcessMemory().convention(js.getDevServer().getProcessMemory());
             task.getProperties().putAll(js.getProperties());
             task.getServerClasspath().from(configuration);
diff --git a/tools/gradle/src/main/java/org/teavm/gradle/tasks/JavaScriptDevServerTask.java b/tools/gradle/src/main/java/org/teavm/gradle/tasks/JavaScriptDevServerTask.java
index f72e7fb94..ed0b03ae6 100644
--- a/tools/gradle/src/main/java/org/teavm/gradle/tasks/JavaScriptDevServerTask.java
+++ b/tools/gradle/src/main/java/org/teavm/gradle/tasks/JavaScriptDevServerTask.java
@@ -29,6 +29,7 @@ import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.TaskAction;
 import org.gradle.internal.logging.progress.ProgressLoggerFactory;
+import org.teavm.gradle.api.JSModuleType;
 
 public abstract class JavaScriptDevServerTask extends DefaultTask {
     @Classpath
@@ -50,6 +51,10 @@ public abstract class JavaScriptDevServerTask extends DefaultTask {
     @Optional
     public abstract ListProperty<String> getPreservedClasses();
 
+    @Input
+    @Optional
+    public abstract Property<JSModuleType> getJsModuleType();
+
     @Input
     public abstract Property<String> getMainClass();
 
@@ -111,6 +116,9 @@ public abstract class JavaScriptDevServerTask extends DefaultTask {
 
         pm.setProperties(getProperties().get());
         pm.setPreservedClasses(getPreservedClasses().get());
+        if (getJsModuleType().isPresent()) {
+            pm.setJsModuleType(getJsModuleType().get());
+        }
 
         pm.setServerClasspath(getServerClasspath().getFiles());
         pm.setMainClass(getMainClass().get());
diff --git a/tools/gradle/src/main/java/org/teavm/gradle/tasks/ProjectDevServerManager.java b/tools/gradle/src/main/java/org/teavm/gradle/tasks/ProjectDevServerManager.java
index f744af229..fca74b25d 100644
--- a/tools/gradle/src/main/java/org/teavm/gradle/tasks/ProjectDevServerManager.java
+++ b/tools/gradle/src/main/java/org/teavm/gradle/tasks/ProjectDevServerManager.java
@@ -43,6 +43,7 @@ import org.teavm.common.json.JsonArrayValue;
 import org.teavm.common.json.JsonObjectValue;
 import org.teavm.common.json.JsonParser;
 import org.teavm.common.json.JsonValue;
+import org.teavm.gradle.api.JSModuleType;
 
 public class ProjectDevServerManager {
     private Set<File> serverClasspath = new LinkedHashSet<>();
@@ -51,6 +52,7 @@ public class ProjectDevServerManager {
     private String targetFilePath;
     private Map<String, String> properties = new LinkedHashMap<>();
     private Set<String> preservedClasses = new LinkedHashSet<>();
+    private JSModuleType jsModuleType;
     private String mainClass;
     private boolean stackDeobfuscated;
     private boolean indicator;
@@ -79,6 +81,7 @@ public class ProjectDevServerManager {
     private String runningTargetFilePath;
     private Map<String, String> runningProperties = new HashMap<>();
     private Set<String> runningPreservedClasses = new HashSet<>();
+    private JSModuleType runningJsModuleType;
     private String runningMainClass;
     private boolean runningStackDeobfuscated;
     private boolean runningIndicator;
@@ -114,6 +117,10 @@ public class ProjectDevServerManager {
         this.preservedClasses.addAll(preservedClasses);
     }
 
+    public void setJsModuleType(JSModuleType jsModuleType) {
+        this.jsModuleType = jsModuleType;
+    }
+
     public void setTargetFileName(String targetFileName) {
         this.targetFileName = targetFileName;
     }
@@ -561,6 +568,12 @@ public class ProjectDevServerManager {
         runningPreservedClasses.clear();
         runningPreservedClasses.addAll(preservedClasses);
 
+        if (jsModuleType != null) {
+            command.add("--js-module-type");
+            command.add(jsModuleType.name().toLowerCase().replace('_', '-'));
+        }
+        runningJsModuleType = jsModuleType;
+
         command.add("--");
         command.add(mainClass);
         runningMainClass = mainClass;
@@ -575,6 +588,7 @@ public class ProjectDevServerManager {
                 && Objects.equals(targetFilePath, runningTargetFilePath)
                 && Objects.equals(properties, runningProperties)
                 && Objects.equals(preservedClasses, runningPreservedClasses)
+                && Objects.equals(jsModuleType, runningJsModuleType)
                 && Objects.equals(mainClass, runningMainClass)
                 && stackDeobfuscated == runningStackDeobfuscated
                 && indicator == runningIndicator