diff --git a/src/com/google/javascript/jscomp/AbstractPeepholeOptimization.java b/src/com/google/javascript/jscomp/AbstractPeepholeOptimization.java
index 366cbae33a0..26492f9731c 100644
--- a/src/com/google/javascript/jscomp/AbstractPeepholeOptimization.java
+++ b/src/com/google/javascript/jscomp/AbstractPeepholeOptimization.java
@@ -17,6 +17,7 @@
 package com.google.javascript.jscomp;
 
 import com.google.common.base.Preconditions;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.Node;
 
 /**
@@ -134,7 +135,8 @@ boolean nodeTypeMayHaveSideEffects(Node n) {
    *     ignored when this is true.
    */
   boolean isEcmaScript5OrGreater() {
-    return compiler != null && compiler.getOptions().getLanguageOut().isEs5OrHigher();
+    return compiler != null
+        && compiler.getOptions().getLanguageOut().toFeatureSet().contains(FeatureSet.ES5);
   }
 
   /**
diff --git a/src/com/google/javascript/jscomp/CommandLineRunner.java b/src/com/google/javascript/jscomp/CommandLineRunner.java
index dd9b1a9b674..64cfcb22975 100644
--- a/src/com/google/javascript/jscomp/CommandLineRunner.java
+++ b/src/com/google/javascript/jscomp/CommandLineRunner.java
@@ -31,6 +31,7 @@
 import com.google.javascript.jscomp.CompilerOptions.IsolationMode;
 import com.google.javascript.jscomp.SourceMap.LocationMapping;
 import com.google.javascript.jscomp.deps.ModuleLoader;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.TokenStream;
 import com.google.protobuf.TextFormat;
 import java.io.BufferedReader;
@@ -1688,7 +1689,8 @@ protected CompilerOptions createOptions() {
       options.setForceLibraryInjection(flags.forceInjectLibraries);
     }
 
-    options.rewritePolyfills = flags.rewritePolyfills && options.getLanguageIn().isEs6OrHigher();
+    options.rewritePolyfills =
+        flags.rewritePolyfills && options.getLanguageIn().toFeatureSet().contains(FeatureSet.ES6);
 
     if (!flags.translationsFile.isEmpty()) {
       try {
diff --git a/src/com/google/javascript/jscomp/CompilerOptions.java b/src/com/google/javascript/jscomp/CompilerOptions.java
index bb82158194a..3f2f1acd46e 100644
--- a/src/com/google/javascript/jscomp/CompilerOptions.java
+++ b/src/com/google/javascript/jscomp/CompilerOptions.java
@@ -3015,25 +3015,10 @@ boolean isDefaultStrict() {
       }
     }
 
-    /** Whether this is ECMAScript 5 or higher. */
-    @Deprecated
-    public boolean isEs5OrHigher() {
-      Preconditions.checkState(this != NO_TRANSPILE);
-      return this != LanguageMode.ECMASCRIPT3;
-    }
-
     /** Whether this is ECMAScript 6 or higher. */
     @Deprecated
     public boolean isEs6OrHigher() {
-      Preconditions.checkState(this != NO_TRANSPILE);
-      switch (this) {
-        case ECMASCRIPT3:
-        case ECMASCRIPT5:
-        case ECMASCRIPT5_STRICT:
-          return false;
-        default:
-          return true;
-      }
+      return this.toFeatureSet().contains(FeatureSet.ES6);
     }
 
     public static LanguageMode fromString(String value) {
diff --git a/src/com/google/javascript/jscomp/CompilerOptionsPreprocessor.java b/src/com/google/javascript/jscomp/CompilerOptionsPreprocessor.java
index 0a07760c5ae..eea2f1fdfe3 100644
--- a/src/com/google/javascript/jscomp/CompilerOptionsPreprocessor.java
+++ b/src/com/google/javascript/jscomp/CompilerOptionsPreprocessor.java
@@ -17,6 +17,7 @@
 
 import static com.google.common.base.Strings.isNullOrEmpty;
 
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.jscomp.parsing.parser.util.format.SimpleFormat;
 
 /**
@@ -47,8 +48,9 @@ static void preprocess(CompilerOptions options) {
           + "remove_unused_prototype_props to be turned on.");
     }
 
-    if (options.getLanguageOut().isEs6OrHigher()
-        && !options.skipNonTranspilationPasses && !options.skipTranspilationAndCrash) {
+    if (options.getLanguageOut().toFeatureSet().contains(FeatureSet.ES6)
+        && !options.skipNonTranspilationPasses
+        && !options.skipTranspilationAndCrash) {
       throw new InvalidOptionsException(
           "ES6 is only supported for transpilation to a lower ECMAScript"
           + " version. Set --language_out to ES3, ES5, or ES5_STRICT.");
@@ -71,7 +73,7 @@ static void preprocess(CompilerOptions options) {
     }
 
     if (options.dartPass) {
-      if (!options.getLanguageOut().isEs5OrHigher()) {
+      if (!options.getLanguageOut().toFeatureSet().contains(FeatureSet.ES5)) {
         throw new InvalidOptionsException("Dart requires --language_out=ES5 or higher.");
       }
       // --dart_pass does not support type-aware property renaming yet.
diff --git a/src/com/google/javascript/jscomp/ConvertToDottedProperties.java b/src/com/google/javascript/jscomp/ConvertToDottedProperties.java
index be6d6f73a92..f32838a362c 100644
--- a/src/com/google/javascript/jscomp/ConvertToDottedProperties.java
+++ b/src/com/google/javascript/jscomp/ConvertToDottedProperties.java
@@ -16,9 +16,8 @@
 
 package com.google.javascript.jscomp;
 
-
-import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
 import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.IR;
 import com.google.javascript.rhino.Node;
 
@@ -48,7 +47,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
       case GETTER_DEF:
       case SETTER_DEF:
       case STRING_KEY:
-        if (NodeUtil.isValidPropertyName(LanguageMode.ECMASCRIPT3, n.getString())) {
+        if (NodeUtil.isValidPropertyName(FeatureSet.ES3, n.getString())) {
           if (n.getBooleanProp(Node.QUOTED_PROP)) {
             n.putBooleanProp(Node.QUOTED_PROP, false);
             compiler.reportChangeToEnclosingScope(n);
@@ -59,8 +58,7 @@ public void visit(NodeTraversal t, Node n, Node parent) {
       case GETELEM:
         Node left = n.getFirstChild();
         Node right = left.getNext();
-        if (right.isString()
-            && NodeUtil.isValidPropertyName(LanguageMode.ECMASCRIPT3, right.getString())) {
+        if (right.isString() && NodeUtil.isValidPropertyName(FeatureSet.ES3, right.getString())) {
           n.removeChild(left);
           n.removeChild(right);
           Node newGetProp = IR.getprop(left, right);
diff --git a/src/com/google/javascript/jscomp/DartSuperAccessorsPass.java b/src/com/google/javascript/jscomp/DartSuperAccessorsPass.java
index fdf32e1c1ef..47d9649c3e6 100644
--- a/src/com/google/javascript/jscomp/DartSuperAccessorsPass.java
+++ b/src/com/google/javascript/jscomp/DartSuperAccessorsPass.java
@@ -16,6 +16,7 @@
 package com.google.javascript.jscomp;
 
 import com.google.common.base.Preconditions;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.IR;
 import com.google.javascript.rhino.Node;
 
@@ -50,7 +51,8 @@ public DartSuperAccessorsPass(AbstractCompiler compiler) {
 
     this.renameProperties = options.propertyRenaming == PropertyRenamingPolicy.ALL_UNQUOTED;
 
-    Preconditions.checkState(options.getLanguageOut().isEs5OrHigher(),
+    Preconditions.checkState(
+        options.getLanguageOut().toFeatureSet().contains(FeatureSet.ES5),
         "Dart super accessors pass requires ES5+ output");
 
     // We currently rely on JSCompiler_renameProperty, which is not type-aware.
diff --git a/src/com/google/javascript/jscomp/DefaultPassConfig.java b/src/com/google/javascript/jscomp/DefaultPassConfig.java
index 4ef45399ded..42b195712bb 100644
--- a/src/com/google/javascript/jscomp/DefaultPassConfig.java
+++ b/src/com/google/javascript/jscomp/DefaultPassConfig.java
@@ -368,7 +368,7 @@ protected List<PassFactory> getChecks() {
 
     // It's important that the Dart super accessors pass run *before* es6ConvertSuper,
     // which is a "late" ES6 pass. This is enforced in the assertValidOrder method.
-    if (options.dartPass && !options.getLanguageOut().isEs6OrHigher()) {
+    if (options.dartPass && !options.getLanguageOut().toFeatureSet().contains(FeatureSet.ES6)) {
       checks.add(dartSuperAccessorsPass);
     }
 
@@ -911,7 +911,7 @@ protected List<PassFactory> getOptimizations() {
     passes.add(sanityCheckVars);
 
     // Raise to ES6, if allowed
-    if (options.getLanguageOut().isEs6OrHigher()) {
+    if (options.getLanguageOut().toFeatureSet().contains(FeatureSet.ES6)) {
       passes.add(optimizeToEs6);
     }
 
diff --git a/src/com/google/javascript/jscomp/NodeUtil.java b/src/com/google/javascript/jscomp/NodeUtil.java
index d2e0d323f3c..26fb89f64dc 100644
--- a/src/com/google/javascript/jscomp/NodeUtil.java
+++ b/src/com/google/javascript/jscomp/NodeUtil.java
@@ -22,6 +22,8 @@
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableSet;
 import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
 import com.google.javascript.rhino.IR;
 import com.google.javascript.rhino.InputId;
 import com.google.javascript.rhino.JSDocInfo;
@@ -3507,10 +3509,13 @@ static boolean isValidSimpleName(String name) {
         && isLatin(name);
   }
 
-  /**
-   * Determines whether the given name is a valid qualified name.
-   */
+  @Deprecated
   public static boolean isValidQualifiedName(LanguageMode mode, String name) {
+    return isValidQualifiedName(mode.toFeatureSet(), name);
+  }
+
+  /** Determines whether the given name is a valid qualified name. */
+  public static boolean isValidQualifiedName(FeatureSet mode, String name) {
     if (name.endsWith(".") || name.startsWith(".")) {
       return false;
     }
@@ -3525,14 +3530,14 @@ public static boolean isValidQualifiedName(LanguageMode mode, String name) {
   }
 
   /**
-   * Determines whether the given name can appear on the right side of
-   * the dot operator. Many properties (like reserved words) cannot, in ES3.
+   * Determines whether the given name can appear on the right side of the dot operator. Many
+   * properties (like reserved words) cannot, in ES3.
    */
-  static boolean isValidPropertyName(LanguageMode mode, String name) {
+  static boolean isValidPropertyName(FeatureSet mode, String name) {
     if (isValidSimpleName(name)) {
       return true;
     } else {
-      return mode.isEs5OrHigher() && TokenStream.isKeyword(name);
+      return mode.contains(Feature.KEYWORDS_AS_PROPERTIES) && TokenStream.isKeyword(name);
     }
   }
 
diff --git a/src/com/google/javascript/jscomp/ProcessClosurePrimitives.java b/src/com/google/javascript/jscomp/ProcessClosurePrimitives.java
index 8105ed052d9..cdb3d250c03 100644
--- a/src/com/google/javascript/jscomp/ProcessClosurePrimitives.java
+++ b/src/com/google/javascript/jscomp/ProcessClosurePrimitives.java
@@ -1043,7 +1043,8 @@ private boolean verifyProvide(NodeTraversal t, Node methodName, Node arg) {
       return false;
     }
 
-    if (!NodeUtil.isValidQualifiedName(compiler.getOptions().getLanguageIn(), arg.getString())) {
+    if (!NodeUtil.isValidQualifiedName(
+        compiler.getOptions().getLanguageIn().toFeatureSet(), arg.getString())) {
       compiler.report(t.makeError(arg, INVALID_PROVIDE_ERROR,
           arg.getString(), compiler.getOptions().getLanguageIn().toString()));
       return false;
@@ -1077,7 +1078,8 @@ private boolean verifyDefine(NodeTraversal t,
     }
 
     String name = args.getString();
-    if (!NodeUtil.isValidQualifiedName(compiler.getOptions().getLanguageIn(), name)) {
+    if (!NodeUtil.isValidQualifiedName(
+        compiler.getOptions().getLanguageIn().toFeatureSet(), name)) {
       compiler.report(t.makeError(args, INVALID_DEFINE_NAME_ERROR, name));
       return false;
     }
diff --git a/src/com/google/javascript/jscomp/ProcessCommonJSModules.java b/src/com/google/javascript/jscomp/ProcessCommonJSModules.java
index 4c989bab121..7b7169cbd9e 100644
--- a/src/com/google/javascript/jscomp/ProcessCommonJSModules.java
+++ b/src/com/google/javascript/jscomp/ProcessCommonJSModules.java
@@ -1150,7 +1150,7 @@ private String getExportedName(NodeTraversal t, Node n, Var var) {
             if (key.isStringKey()
                 && !key.isQuotedString()
                 && NodeUtil.isValidPropertyName(
-                    compiler.getOptions().getLanguageIn(), key.getString())) {
+                    compiler.getOptions().getLanguageIn().toFeatureSet(), key.getString())) {
               if (key.hasChildren()) {
                 if (key.getFirstChild().isQualifiedName()) {
                   if (key.getFirstChild() == n) {
diff --git a/src/com/google/javascript/jscomp/TranspilationPasses.java b/src/com/google/javascript/jscomp/TranspilationPasses.java
index 0170ac17bfe..6c8c85c926a 100644
--- a/src/com/google/javascript/jscomp/TranspilationPasses.java
+++ b/src/com/google/javascript/jscomp/TranspilationPasses.java
@@ -205,7 +205,7 @@ static boolean isScriptEs6ImplOrHigher(Node script) {
    * @param callbacks The callbacks that should be invoked if a file has ES6 features.
    */
   static void processCheck(AbstractCompiler compiler, Node combinedRoot, Callback... callbacks) {
-    if (compiler.getOptions().getLanguageIn().isEs6OrHigher()) {
+    if (compiler.getOptions().getLanguageIn().toFeatureSet().contains(FeatureSet.ES6)) {
       for (Node singleRoot : combinedRoot.children()) {
         if (isScriptEs6ImplOrHigher(singleRoot)) {
           for (Callback callback : callbacks) {
@@ -225,7 +225,7 @@ static void processCheck(AbstractCompiler compiler, Node combinedRoot, Callback.
    * @param callbacks The callbacks that should be invoked if the file has ES6 features.
    */
   static void hotSwapCheck(AbstractCompiler compiler, Node scriptRoot, Callback... callbacks) {
-    if (compiler.getOptions().getLanguageIn().isEs6OrHigher()) {
+    if (compiler.getOptions().getLanguageIn().toFeatureSet().contains(FeatureSet.ES6)) {
       if (isScriptEs6ImplOrHigher(scriptRoot)) {
         for (Callback callback : callbacks) {
           NodeTraversal.traverseEs6(compiler, scriptRoot, callback);
diff --git a/src/com/google/javascript/jscomp/VariableReferenceCheck.java b/src/com/google/javascript/jscomp/VariableReferenceCheck.java
index 3902e7aa965..c8b246f8df8 100644
--- a/src/com/google/javascript/jscomp/VariableReferenceCheck.java
+++ b/src/com/google/javascript/jscomp/VariableReferenceCheck.java
@@ -20,6 +20,7 @@
 import com.google.common.collect.Sets;
 import com.google.javascript.jscomp.NodeTraversal.AbstractShallowCallback;
 import com.google.javascript.jscomp.ReferenceCollectingCallback.Behavior;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.JSDocInfo;
 import com.google.javascript.rhino.Node;
 import com.google.javascript.rhino.Token;
@@ -95,7 +96,7 @@ private boolean shouldProcess(Node root) {
     if (!forTranspileOnly) {
       return true;
     }
-    if (compiler.getOptions().getLanguageIn().isEs6OrHigher()) {
+    if (compiler.getOptions().getLanguageIn().toFeatureSet().contains(FeatureSet.ES6)) {
       for (Node singleRoot : root.children()) {
         if (TranspilationPasses.isScriptEs6ImplOrHigher(singleRoot)) {
           return true;
@@ -117,7 +118,7 @@ compiler, new ReferenceCheckingBehavior(), new Es6SyntacticScopeCreator(compiler
   @Override
   public void hotSwapScript(Node scriptRoot, Node originalRoot) {
     if (!forTranspileOnly
-        || (compiler.getOptions().getLanguageIn().isEs6OrHigher()
+        || (compiler.getOptions().getLanguageIn().toFeatureSet().contains(FeatureSet.ES6)
             && TranspilationPasses.isScriptEs6ImplOrHigher(scriptRoot))) {
       new ReferenceCollectingCallback(
               compiler, new ReferenceCheckingBehavior(), new Es6SyntacticScopeCreator(compiler))
diff --git a/test/com/google/javascript/jscomp/NewTypeInferenceTestBase.java b/test/com/google/javascript/jscomp/NewTypeInferenceTestBase.java
index e86f2e410ab..14f62f97f0e 100644
--- a/test/com/google/javascript/jscomp/NewTypeInferenceTestBase.java
+++ b/test/com/google/javascript/jscomp/NewTypeInferenceTestBase.java
@@ -22,6 +22,7 @@
 
 import com.google.common.collect.ImmutableList;
 import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.IR;
 import com.google.javascript.rhino.InputId;
 import com.google.javascript.rhino.Node;
@@ -222,8 +223,7 @@ private final void parseAndTypeCheck(String externs, String js) {
       passes.add(makePassFactory("convertEs6TypedToEs6",
               new Es6TypedToEs6Converter(compiler)));
     }
-    if (compilerOptions.getLanguageIn().isEs6OrHigher()
-        && !compilerOptions.getLanguageOut().isEs6OrHigher()) {
+    if (compilerOptions.needsTranspilationFrom(FeatureSet.ES6)) {
       TranspilationPasses.addEs2017Passes(passes);
       TranspilationPasses.addEs6EarlyPasses(passes);
       TranspilationPasses.addEs6LatePasses(passes);
diff --git a/test/com/google/javascript/jscomp/NodeUtilTest.java b/test/com/google/javascript/jscomp/NodeUtilTest.java
index c8ac4f84cd9..9fa14e2ed48 100644
--- a/test/com/google/javascript/jscomp/NodeUtilTest.java
+++ b/test/com/google/javascript/jscomp/NodeUtilTest.java
@@ -25,6 +25,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.rhino.IR;
 import com.google.javascript.rhino.JSTypeExpression;
 import com.google.javascript.rhino.Node;
@@ -2587,10 +2588,10 @@ private static Node getNameNode(Node n, String name) {
   }
 
   private static boolean isValidPropertyName(String s) {
-    return NodeUtil.isValidPropertyName(LanguageMode.ECMASCRIPT3, s);
+    return NodeUtil.isValidPropertyName(FeatureSet.ES3, s);
   }
 
   private static boolean isValidQualifiedName(String s) {
-    return NodeUtil.isValidQualifiedName(LanguageMode.ECMASCRIPT3, s);
+    return NodeUtil.isValidQualifiedName(FeatureSet.ES3, s);
   }
 }
diff --git a/test/com/google/javascript/jscomp/TypeCheckTest.java b/test/com/google/javascript/jscomp/TypeCheckTest.java
index 3bdf6433344..c6f317a2dc8 100644
--- a/test/com/google/javascript/jscomp/TypeCheckTest.java
+++ b/test/com/google/javascript/jscomp/TypeCheckTest.java
@@ -24,6 +24,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.javascript.jscomp.CompilerOptions.LanguageMode;
+import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.jscomp.type.ClosureReverseAbstractInterpreter;
 import com.google.javascript.jscomp.type.SemanticReverseAbstractInterpreter;
 import com.google.javascript.rhino.IR;
@@ -17849,7 +17850,7 @@ private TypeCheckResult parseAndTypeCheckWithScope(
         Joiner.on(", ").join(compiler.getErrors()),
         0, compiler.getErrorCount());
 
-    if (compiler.getOptions().getLanguageIn().isEs6OrHigher()) {
+    if (compiler.getOptions().getLanguageIn().toFeatureSet().contains(FeatureSet.ES6)) {
       List<PassFactory> passes = new ArrayList<>();
       TranspilationPasses.addEs2017Passes(passes);
       TranspilationPasses.addEs6EarlyPasses(passes);