Check for index-out-of-bound in elementAt function (KT-30051)

libraries/stdlib/js/src/generated/_StringsJs.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license 
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.text
+
+//
+// NOTE: THIS FILE IS AUTO-GENERATED by the GenerateStandardLib.kt
+// See: https://github.com/JetBrains/kotlin/tree/master/libraries/stdlib
+//
+
+import kotlin.js.*
+
+/**
+ * Returns a character at the given [index] or throws an [IndexOutOfBoundsException] if the [index] is out of bounds of this char sequence.
+ * 
+ * @sample samples.collections.Collections.Elements.elementAt
+ */
+public actual fun CharSequence.elementAt(index: Int): Char {
+    return elementAtOrElse(index) { throw IndexOutOfBoundsException("index: $index, length: $length}") }
+}
+