Add isEmpty, isBlank methods and their nullable and negating couterparts.

js/js.libraries/src/core/stringsCode.kt

@@ -28,6 +28,9 @@ public inline fun String.matches(regex : String) : Boolean {
     return result != null && result.size() > 0
 }
 
+
+public fun String.isBlank(): Boolean = length() == 0 || matches("^[\\s\\xA0]+$")
+
 public fun String.equals(anotherString: String, ignoreCase: Boolean = false): Boolean =
         if (!ignoreCase)
             this == anotherString

libraries/stdlib/src/kotlin/text/Strings.kt

@@ -1,6 +1,7 @@
 package kotlin
 
 import java.util.NoSuchElementException
+import kotlin.platform.platformName
 
 /** Returns the string with leading and trailing text matching the given string removed */
 deprecated("Use removeEnclosing(text, text) or removePrefix(text).removeSuffix(text)")
@@ -146,8 +147,49 @@ public fun String.padEnd(length: Int, padChar: Char = ' '): String {
 }
 
 /** Returns true if the string is not null and not empty */
+deprecated("Use isNotNullOrEmpty for nullable strings.")
+platformName("isNotEmptyNullable")
 public fun String?.isNotEmpty(): Boolean = this != null && this.length() > 0
 
+/**
+ * Return `true` if this nullable string is either null or empty.
+ */
+public fun String?.isNullOrEmpty(): Boolean = this == null || this.length() == 0
+
+/**
+ * Return `true` if this nullable string is neither null nor empty.
+ */
+public fun String?.isNotNullOrEmpty(): Boolean = this != null && this.length() > 0
+
+/**
+ * Returns `true` if this string is empty (contains no characters).
+ */
+public fun String.isEmpty(): Boolean = length() == 0
+
+/**
+ * Returns `true` if this string is not empty.
+ */
+public fun String.isNotEmpty(): Boolean = length() > 0
+
+// implemented differently in JVM and JS
+//public fun String.isBlank(): Boolean = length() == 0 || all { it.isWhitespace() }
+
+
+/**
+ * Returns `true` if this string is not empty and contains some characters except of whitespace characters.
+ */
+public fun String.isNotBlank(): Boolean = !isBlank()
+
+/**
+ * Returns `true` if this nullable string is either null or empty or consists solely of whitespace characters.
+ */
+public fun String?.isNullOrBlank(): Boolean = this == null || this.isBlank()
+
+/**
+ * Returns `true` if this nullable string is neither null nor empty, and contains some characters except of whitespace characters.
+ */
+public fun String?.isNotNullOrBlank(): Boolean = this != null && !this.isBlank()
+
 /**
  * Iterator for characters of given CharSequence
  */

libraries/stdlib/src/kotlin/text/StringsJVM.kt

@@ -275,10 +275,9 @@ public fun String.getChars(srcBegin: Int, srcEnd: Int, dst: CharArray, dstBegin:
 public fun String.intern(): String = (this as java.lang.String).intern()
 
 /**
- * Returns `true` if this string is empty (contains no characters).
+ * Returns `true` if this string is empty or consists solely of whitespace characters.
  */
-public fun String.isEmpty(): Boolean = (this as java.lang.String).isEmpty()
-
+public fun String.isBlank(): Boolean = length() == 0 || all { it.isWhitespace() }
 
 /**
  * Returns `true` if this string matches the given regular expression.

libraries/stdlib/test/text/StringTest.kt

@@ -3,8 +3,32 @@ package test.text
 import kotlin.test.*
 import org.junit.Test as test
 
+// could not be local inside isEmptyAndBlank, because non-toplevel declarations is not yet supported for JS
+class IsEmptyCase(val value: String?, val isNull: Boolean = false, val isEmpty: Boolean = false, val isBlank: Boolean = false)
+
 class StringTest {
 
+    test fun isEmptyAndBlank() {
+
+        val cases = listOf(
+            IsEmptyCase(null,              isNull = true),
+            IsEmptyCase("",                isEmpty = true, isBlank = true),
+            IsEmptyCase("  \r\n\t\u00A0",  isBlank = true),
+            IsEmptyCase(" Some ")
+        )
+
+        for (case in cases) {
+            assertEquals(case.isNull || case.isEmpty, case.value.isNullOrEmpty(), "failed for case '${case.value}'")
+            assertEquals(case.isNull || case.isBlank, case.value.isNullOrBlank(), "failed for case '${case.value}'")
+            if (case.value != null)
+            {
+                assertEquals(case.isEmpty, case.value.isEmpty(), "failed for case '${case.value}'")
+                assertEquals(case.isBlank, case.value.isBlank(), "failed for case '${case.value}'")
+            }
+
+        }
+    }
+
     test fun startsWithString() {
         assertTrue("abcd".startsWith("ab"))
         assertTrue("abcd".startsWith("abcd"))