diff --git a/js/js.libraries/src/core/string.kt b/js/js.libraries/src/core/string.kt
index 8f889d08437..7c202f42c42 100644
--- a/js/js.libraries/src/core/string.kt
+++ b/js/js.libraries/src/core/string.kt
@@ -4,12 +4,21 @@ native public fun String.toUpperCase() : String = noImpl
 
 native public fun String.toLowerCase() : String = noImpl
 
+// TODO: make internal
 native("indexOf")
 public fun String.nativeIndexOf(str : String, fromIndex : Int) : Int = noImpl
 
+// TODO: make internal
 native("lastIndexOf")
 public fun String.nativeLastIndexOf(str : String, fromIndex : Int) : Int = noImpl
 
+// TODO: make internal
+native("startsWith")
+public fun String.nativeStartsWith(s: String, position: Int): Boolean = noImpl
+// TODO: make internal
+native("endsWith")
+public fun String.nativeEndsWith(s: String): Boolean = noImpl
+
 library("splitString")
 public fun String.splitWithRegex(regex: String): Array<String> = noImpl
 
diff --git a/js/js.libraries/src/core/stringsCode.kt b/js/js.libraries/src/core/stringsCode.kt
index eadadd4e1aa..a11da1e350d 100644
--- a/js/js.libraries/src/core/stringsCode.kt
+++ b/js/js.libraries/src/core/stringsCode.kt
@@ -1,25 +1,38 @@
 package kotlin.js
 
+// TODO: make internal
 public inline fun String.nativeIndexOf(ch : Char, fromIndex : Int) : Int = nativeIndexOf(ch.toString(), fromIndex)
 public inline fun String.nativeLastIndexOf(ch : Char, fromIndex : Int) : Int = nativeLastIndexOf(ch.toString(), fromIndex)
 
 /**
  * Returns `true` if this string starts with the specified prefix.
  */
-public fun String.startsWith(prefix: String, ignoreCase: Boolean = false): Boolean =
-        regionMatches(0, prefix, 0, prefix.length(), ignoreCase)
+public fun String.startsWith(prefix: String, ignoreCase: Boolean = false): Boolean {
+    if (!ignoreCase)
+        return nativeStartsWith(prefix, 0)
+    else
+        return regionMatches(0, prefix, 0, prefix.length(), ignoreCase)
+}
 
 /**
  * Returns `true` if a substring of this string starting at the specified offset [thisOffset] starts with the specified prefix.
  */
-public fun String.startsWith(prefix: String, thisOffset: Int, ignoreCase: Boolean = false): Boolean =
-        regionMatches(thisOffset, prefix, 0, prefix.length(), ignoreCase)
+public fun String.startsWith(prefix: String, thisOffset: Int, ignoreCase: Boolean = false): Boolean {
+    if (!ignoreCase)
+        return nativeStartsWith(prefix, thisOffset)
+    else
+        return regionMatches(thisOffset, prefix, 0, prefix.length(), ignoreCase)
+}
 
 /**
  * Returns `true` if this string ends with the specified suffix.
  */
-public fun String.endsWith(suffix: String, ignoreCase: Boolean = false): Boolean =
-        regionMatches(length() - suffix.length(), suffix, 0, suffix.length(), ignoreCase = true)
+public fun String.endsWith(suffix: String, ignoreCase: Boolean = false): Boolean {
+    if (!ignoreCase)
+        return nativeEndsWith(suffix)
+    else
+        return regionMatches(length() - suffix.length(), suffix, 0, suffix.length(), ignoreCase)
+}
 
 
 
diff --git a/libraries/stdlib/test/text/StringTest.kt b/libraries/stdlib/test/text/StringTest.kt
index c4ad0f771be..eda6fa62d3a 100644
--- a/libraries/stdlib/test/text/StringTest.kt
+++ b/libraries/stdlib/test/text/StringTest.kt
@@ -39,6 +39,7 @@ class StringTest {
         assertTrue("some".startsWith(""))
         assertTrue("".startsWith(""))
 
+        assertFalse("abcd".startsWith("aB", ignoreCase = false))
         assertTrue("abcd".startsWith("aB", ignoreCase = true))
     }
 
@@ -46,6 +47,7 @@ class StringTest {
         assertTrue("abcd".endsWith("d"))
         assertTrue("abcd".endsWith("abcd"))
         assertFalse("abcd".endsWith("b"))
+        assertFalse("strö".endsWith("RÖ", ignoreCase = false))
         assertTrue("strö".endsWith("RÖ", ignoreCase = true))
         assertFalse("".endsWith("a"))
         assertTrue("some".endsWith(""))
@@ -55,6 +57,7 @@ class StringTest {
     test fun startsWithChar() {
         assertTrue("abcd".startsWith('a'))
         assertFalse("abcd".startsWith('b'))
+        assertFalse("abcd".startsWith('A', ignoreCase = false))
         assertTrue("abcd".startsWith('A', ignoreCase = true))
         assertFalse("".startsWith('a'))
     }
@@ -62,6 +65,7 @@ class StringTest {
     test fun endsWithChar() {
         assertTrue("abcd".endsWith('d'))
         assertFalse("abcd".endsWith('b'))
+        assertFalse("strö".endsWith('Ö', ignoreCase = false))
         assertTrue("strö".endsWith('Ö', ignoreCase = true))
         assertFalse("".endsWith('a'))
     }