Add string.trimLeft/trimRight.

sdk/lib/_internal/lib/js_string.dart

Index: sdk/lib/_internal/lib/js_string.dart
diff --git a/sdk/lib/_internal/lib/js_string.dart b/sdk/lib/_internal/lib/js_string.dart
index 4055647e46b5407a8260eac22f03a0469332feb3..b6d54876c9d7e2e742b4c84b45d17e12a4d47abe 100644
--- a/sdk/lib/_internal/lib/js_string.dart
+++ b/sdk/lib/_internal/lib/js_string.dart
@@ -175,6 +175,37 @@ class JSString extends Interceptor implements String, JSIndexable {
     }
   }
 
+  /// Finds the index of the first non-whitespace character, or the
+  /// end of the string.
+  static int _skipLeadingWhitespace(String string, int index) {
+    while (index < string.length) {
+      int codeUnit = string.codeUnitAt(index);
+      if (codeUnit == SPACE ||
+          codeUnit == CARRIAGE_RETURN ||
+          _isWhitespace(codeUnit)) {
+        index++;
+      } else {
+        break;
+      }
+    }
+    return index;
+  }
+
+  /// Finds the index after the the last non-whitespace character, or 0.
+  static int _skipTrailingWhitespace(String string, int index) {
+    while (index > 0) {
+      int codeUnit = string.codeUnitAt(index - 1);
+      if (codeUnit == SPACE ||
+          codeUnit == CARRIAGE_RETURN ||
+          _isWhitespace(codeUnit)) {
+        index--;
+      } else {
+        break;
+      }
+    }
+    return index;
+  }
+
   // Dart2js can't use JavaScript trim, because JavaScript does not trim
   // the NEXT LINE character (0x85) and BOMs (0xFEFF).
   String trim() {
@@ -191,17 +222,7 @@ class JSString extends Interceptor implements String, JSIndexable {
     int firstCode = result.codeUnitAt(0);
     int startIndex = 0;
     if (firstCode == NEL || firstCode == BOM) {

[Søren Gjesse, 2014/03/10 16:50:03]

What if there are several BOM/NEL characters? Shouldn't we handle that as well,
or is that a completely broken string?

[Lasse Reichstein Nielsen, 2014/03/11 10:36:29]

Those are handled by _skipLeadingWhitespace. They are just not handled by JS
trim. We try JS trim first (because usually it's just spaces and tabs), and if
there is a NEL or BOM left, we skip to our own, probably slower, method that
handles everything.

-      startIndex++;
-      while (startIndex < result.length) {
-        int codeUnit = result.codeUnitAt(startIndex);
-        if (codeUnit == SPACE ||
-            codeUnit == CARRIAGE_RETURN ||
-            _isWhitespace(codeUnit)) {
-          startIndex++;
-        } else {
-          break;
-        }
-      }
+      startIndex = _skipLeadingWhitespace(this, 1);
       if (startIndex == result.length) return "";
     }
 
@@ -210,22 +231,62 @@ class JSString extends Interceptor implements String, JSIndexable {
     // Therefore we don't need to verify that endIndex > startIndex.
     int lastCode = result.codeUnitAt(endIndex - 1);
     if (lastCode == NEL || lastCode == BOM) {
-      endIndex--;
-      while (true) {
-        int codeUnit = result.codeUnitAt(endIndex - 1);
-        if (codeUnit == SPACE ||
-            codeUnit == CARRIAGE_RETURN ||
-            _isWhitespace(codeUnit)) {
-          endIndex--;
-        } else {
-          break;
-        }
-      }
+      endIndex = _skipTrailingWhitespace(this, endIndex - 1);
     }
     if (startIndex == 0 && endIndex == result.length) return result;
     return JS('String', r'#.substring(#, #)', result, startIndex, endIndex);
   }
 
+  // Dart2js can't use JavaScript trim, because JavaScript does not trim
+  // the NEXT LINE character (0x85) and BOMs (0xFEFF).
+  String trimLeft() {
+    const int CARRIAGE_RETURN = 0x0D;
+    const int SPACE = 0x20;
+    const int NEL = 0x85;
+    const int BOM = 0xFEFF;
+
+    // Start by doing JS trim. Then check if it leaves a NEL or BOM at
+    // either end of the string.
+    String result = JS('String', '#.trimLeft()', this);

[Lasse Reichstein Nielsen, 2014/03/10 13:27:50]

Just checked. "trimLeft" and "trimRight" are not in ES5. They are implemented by
Firefox and Blink, so we might want to use them if they are there. That would
mean changing this to:
 JS('String', '#.trimLeft ? #.trimLeft() : #", this, this, this)
and similar for trimRight.

[Søren Gjesse, 2014/03/10 16:50:03]

Are we even doing that for trim?

[Lasse Reichstein Nielsen, 2014/03/11 10:36:29]

Plain trim is in ES5.
My simple rewrite here wouldn't work, I'll do something large.

+
+    if (result.length == 0) return result;
+    int firstCode = result.codeUnitAt(0);
+    int startIndex = 0;
+    if (firstCode == NEL || firstCode == BOM) {
+      startIndex = _skipLeadingWhitespace(this, 1);
+      if (startIndex == result.length) return "";
+    }
+
+    if (startIndex == 0) return result;
+    return JS('String', r'#.substring(#, #)',
+              result, startIndex, result.length);
+  }
+
+  // Dart2js can't use JavaScript trim, because JavaScript does not trim
+  // the NEXT LINE character (0x85) and BOMs (0xFEFF).
+  String trimRight() {
+    const int CARRIAGE_RETURN = 0x0D;
+    const int SPACE = 0x20;
+    const int NEL = 0x85;
+    const int BOM = 0xFEFF;
+
+    // Start by doing JS trim. Then check if it leaves a NEL or BOM at
+    // either end of the string.
+    String result = JS('String', '#.trimRight()', this);
+
+    if (result.length == 0) return result;
+
+    int endIndex = result.length;
+    // We know that there is at least one character that is non-whitespace.
+    // Therefore we don't need to verify that endIndex > startIndex.
+    int lastCode = result.codeUnitAt(endIndex - 1);
+    if (lastCode == NEL || lastCode == BOM) {
+      endIndex = _skipTrailingWhitespace(this, endIndex - 1);
+    }
+    if (endIndex == result.length) return result;
+    return JS('String', r'#.substring(#, #)', result, 0, endIndex);
+  }
+
   String operator*(int times) {
     if (0 >= times) return '';  // Unnecessary but hoists argument type check.
     if (times == 1 || this.length == 0) return this;