Implement String to/from CharArray conversion (KT-29265)

libraries/stdlib/js/src/kotlin/text/string.kt

@@ -36,6 +36,44 @@ public actual fun String(chars: CharArray, offset: Int, length: Int): String {
     return result
 }
 
+/**
+ * Concatenates characters in this [CharArray] or its subrange into a String.
+ *
+ * @param startIndex the beginning (inclusive) of the subrange of characters, 0 by default.
+ * @param endIndex the end (exclusive) of the subrange of characters, size of this array by default.
+ *
+ * @throws IndexOutOfBoundsException if [startIndex] is less than zero or [endIndex] is greater than the size of this array.
+ * @throws IllegalArgumentException if [startIndex] is greater than [endIndex].
+ */
+@SinceKotlin("1.3")
+@Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
+@ExperimentalStdlibApi
+public actual fun CharArray.concatToString(startIndex: Int = 0, endIndex: Int = this.size): String {
+    AbstractList.checkBoundsIndexes(startIndex, endIndex, this.size)
+    var result = ""
+    for (index in startIndex until endIndex) {
+        result += this[index]
+    }
+    return result
+}
+
+/**
+ * Returns a [CharArray] containing characters of this string or its substring.
+ *
+ * @param startIndex the beginning (inclusive) of the substring, 0 by default.
+ * @param endIndex the end (exclusive) of the substring, length of this string by default.
+ *
+ * @throws IndexOutOfBoundsException if [startIndex] is less than zero or [endIndex] is greater than the length of this string.
+ * @throws IllegalArgumentException if [startIndex] is greater than [endIndex].
+ */
+@SinceKotlin("1.3")
+@Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
+@ExperimentalStdlibApi
+public actual fun String.toCharArray(startIndex: Int = 0, endIndex: Int = this.length): CharArray {
+    AbstractList.checkBoundsIndexes(startIndex, endIndex, length)
+    return CharArray(endIndex - startIndex) { get(startIndex + it) }
+}
+
 /**
  * Returns a copy of this string converted to upper case using the rules of the default locale.
  *