diff --git a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
index 5ac53c3be..f4cdfdd41 100644
--- a/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
+++ b/teavm-classlib/src/main/java/org/teavm/classlib/java/lang/TString.java
@@ -19,6 +19,9 @@ import org.teavm.classlib.impl.charset.*;
 import org.teavm.classlib.java.io.TSerializable;
 import org.teavm.classlib.java.io.TUnsupportedEncodingException;
 import org.teavm.classlib.java.util.TArrays;
+import org.teavm.classlib.java.util.TComparator;
+import org.teavm.classlib.java.util.THashMap;
+import org.teavm.classlib.java.util.TMap;
 import org.teavm.dependency.PluggableDependency;
 import org.teavm.javascript.ni.InjectedBy;
 import org.teavm.javascript.ni.Rename;
@@ -28,8 +31,14 @@ import org.teavm.javascript.ni.Rename;
  * @author Alexey Andreev <konsoletyper@gmail.com>
  */
 public class TString extends TObject implements TSerializable, TComparable<TString>, TCharSequence {
+    public static final TComparator<TString> CASE_INSENSITIVE_ORDER = new TComparator<TString>() {
+        @Override public int compare(TString o1, TString o2) {
+            return o1.compareToIgnoreCase(o2);
+        }
+    };
     private char[] characters;
     private transient int hashCode;
+    private static TMap<TString, TString> pool = new THashMap<>();
 
     public TString() {
         this.characters = new char[0];
@@ -183,6 +192,21 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         return length() - anotherString.length();
     }
 
+    public int compareToIgnoreCase(TString anotherString) {
+        if (this == anotherString) {
+            return 0;
+        }
+        int l = TMath.min(length(), anotherString.length());
+        for (int i = 0; i < l; ++i) {
+            char a = TCharacter.toLowerCase(charAt(i));
+            char b = TCharacter.toLowerCase(anotherString.charAt(i));
+            if (a - b != 0) {
+                return a - b;
+            }
+        }
+        return length() - anotherString.length();
+    }
+
     public boolean startsWith(TString prefix, int toffset) {
         if (toffset + prefix.length() > length()) {
             return false;
@@ -548,4 +572,32 @@ public class TString extends TObject implements TSerializable, TComparable<TStri
         }
         return new TString(codePoints, 0, codePointCount);
     }
+
+    public TString toUpperCase() {
+        if (isEmpty()) {
+            return this;
+        }
+        int[] codePoints = new int[characters.length];
+        int codePointCount = 0;
+        for (int i = 0; i < characters.length; ++i) {
+            if (i == characters.length - 1 || !UTF16Helper.isHighSurrogate(characters[i]) ||
+                    !UTF16Helper.isLowSurrogate(characters[i + 1])) {
+                codePoints[codePointCount++] = TCharacter.toUpperCase(characters[i]);
+            } else {
+                codePoints[codePointCount++] = TCharacter.toUpperCase(UTF16Helper.buildCodePoint(
+                        characters[i], characters[i + 1]));
+                ++i;
+            }
+        }
+        return new TString(codePoints, 0, codePointCount);
+    }
+
+    public TString intern() {
+        TString interned = pool.get(this);
+        if (interned == null) {
+            interned = this;
+            pool.put(interned, interned);
+        }
+        return interned;
+    }
 }
diff --git a/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java b/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
index 5f8e7c15d..fdf5ffdbb 100644
--- a/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
+++ b/teavm-classlib/src/test/java/org/teavm/classlib/java/lang/StringTest.java
@@ -290,4 +290,14 @@ public class StringTest {
     public void makesLowerCase() {
         assertEquals("foo bar", "FoO bAr".toLowerCase());
     }
+
+    @Test
+    public void interns() {
+        assertSame(("ab" + "c").intern(), ("a" + "bc").intern());
+    }
+
+    @Test
+    public void internsConstants() {
+        assertSame("abc", ("a" + "bc").intern());
+    }
 }
diff --git a/teavm-core/src/main/java/org/teavm/javascript/Renderer.java b/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
index 298cfa8d2..eb34438d9 100644
--- a/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
+++ b/teavm-core/src/main/java/org/teavm/javascript/Renderer.java
@@ -34,6 +34,8 @@ import org.teavm.model.*;
  * @author Alexey Andreev
  */
 public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext {
+    private static final MethodReference internRef = new MethodReference("java.lang.String", "intern",
+            ValueType.object("java.lang.String"));
     private static final String variableNames = "abcdefghijkmnopqrstuvwxyz";
     private NamingStrategy naming;
     private SourceWriter writer;
@@ -930,7 +932,7 @@ public class Renderer implements ExprVisitor, StatementVisitor, RenderingContext
             ValueType type = (ValueType)cst;
             return "$rt_cls(" + typeToClsString(naming, type) + ")";
         } else if (cst instanceof String) {
-            return "$rt_str(\"" + escapeString((String)cst) + "\")";
+            return naming.getFullNameFor(internRef) + "($rt_str(\"" + escapeString((String)cst) + "\"))";
         } else if (cst instanceof Long) {
             long value = (Long)cst;
             if (value == 0) {
diff --git a/teavm-core/src/main/java/org/teavm/vm/TeaVM.java b/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
index 9c6a2db5b..d5001f6d7 100644
--- a/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
+++ b/teavm-core/src/main/java/org/teavm/vm/TeaVM.java
@@ -174,6 +174,10 @@ public class TeaVM implements TeaVMHost {
         dependencyChecker.linkMethod(new MethodReference("java.lang.String", "getChars",
                 ValueType.INTEGER, ValueType.INTEGER, ValueType.arrayOf(ValueType.CHARACTER), ValueType.INTEGER,
                 ValueType.VOID), DependencyStack.ROOT).use();
+        MethodDependency internDep = dependencyChecker.linkMethod(new MethodReference("java.lang.String", "intern",
+                ValueType.object("java.lang.String")), DependencyStack.ROOT);
+        internDep.getVariable(0).propagate("java.lang.String");
+        internDep.use();
         dependencyChecker.linkMethod(new MethodReference("java.lang.String", "length", ValueType.INTEGER),
                 DependencyStack.ROOT).use();
         dependencyChecker.linkMethod(new MethodReference("java.lang.Object", new MethodDescriptor("clone",