⚡ port JS String.prototype.slice() method to Dart

lib/src/extensions/decode.dart

@@ -61,9 +61,9 @@ extension _$Decode on QS {
         key = options.decoder(part, charset: charset);
         val = options.strictNullHandling ? null : '';
       } else {
-        key = options.decoder(part.substring(0, pos), charset: charset);
+        key = options.decoder(part.slice(0, pos), charset: charset);
         val = Utils.apply<dynamic>(
-          _parseArrayValue(part.substring(pos + 1), options),
+          _parseArrayValue(part.slice(pos + 1), options),
           (dynamic val) => options.decoder(val, charset: charset),
         );
       }
@@ -109,7 +109,7 @@ extension _$Decode on QS {
       } else {
         obj = Map.of({});
         final String cleanRoot = root.startsWith('[') && root.endsWith(']')
-            ? root.substring(1, root.length - 1)
+            ? root.slice(1, root.length - 1)
             : root;
         final String decodedRoot = options.decodeDotInKeys
             ? cleanRoot.replaceAll('%2E', '.')
@@ -163,8 +163,7 @@ extension _$Decode on QS {
 
     // Get the parent
     Match? segment = options.depth > 0 ? brackets.firstMatch(key) : null;
-    final String parent =
-        segment != null ? key.substring(0, segment.start) : key;
+    final String parent = segment != null ? key.slice(0, segment.start) : key;
 
     // Stash the parent if it exists
     final List<String> keys = [];
@@ -181,13 +180,13 @@ extension _$Decode on QS {
       if (segment != null) {
         keys.add(segment.group(1)!);
         // Update the key to start searching from the next position
-        key = key.substring(segment.end);
+        key = key.slice(segment.end);
       }
     }
 
     // If there's a remainder, just add whatever is left
     if (segment != null) {
-      keys.add('[${key.substring(segment.start)}]');
+      keys.add('[${key.slice(segment.start)}]');
     }
 
     return _parseObject(keys, val, options, valuesParsed);

lib/src/extensions/extensions.dart

@@ -1,3 +1,4 @@
+import 'dart:math' show min;
 import 'package:qs_dart/src/models/undefined.dart';
 
 extension IterableExtension<T> on Iterable<T> {
@@ -9,3 +10,20 @@ extension ListExtension<T> on List<T> {
   /// Returns a new [List] without [Undefined] elements.
   List<T> whereNotUndefined() => where((T el) => el is! Undefined).toList();
 }
+
+extension StringExtension on String {
+  /// Extracts a section of a string and returns a new string.
+  ///
+  /// Modeled after JavaScript's `String.prototype.slice()` method.
+  /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice
+  String slice(int start, [int? end]) {
+    end ??= length;
+    if (end < 0) {
+      end = length + end;
+    }
+    if (start < 0) {
+      start = length + start;
+    }
+    return substring(start, min(end, length));
+  }
+}

lib/src/qs.dart

@@ -5,6 +5,7 @@ import 'package:qs_dart/src/enums/duplicates.dart';
 import 'package:qs_dart/src/enums/format.dart';
 import 'package:qs_dart/src/enums/list_format.dart';
 import 'package:qs_dart/src/enums/sentinel.dart';
+import 'package:qs_dart/src/extensions/extensions.dart';
 import 'package:qs_dart/src/models/decode_options.dart';
 import 'package:qs_dart/src/models/encode_options.dart';
 import 'package:qs_dart/src/models/undefined.dart';

lib/src/utils.dart

@@ -1,6 +1,5 @@
 import 'dart:collection' show SplayTreeMap;
 import 'dart:convert' show latin1, utf8, Encoding;
-import 'dart:math' show min;
 import 'dart:typed_data' show ByteBuffer;
 
 import 'package:collection/collection.dart' show MapEquality;
@@ -205,14 +204,14 @@ final class Utils {
       if (c == 0x25) {
         if (str[i + 1] == 'u') {
           buffer.writeCharCode(
-            int.parse(str.substring(i + 2, i + 6), radix: 16),
+            int.parse(str.slice(i + 2, i + 6), radix: 16),
           );
           i += 6;
           continue;
         }
 
         buffer.writeCharCode(
-          int.parse(str.substring(i + 1, i + 3), radix: 16),
+          int.parse(str.slice(i + 1, i + 3), radix: 16),
         );
         i += 3;
         continue;
@@ -260,9 +259,8 @@ final class Utils {
     final StringBuffer buffer = StringBuffer();
 
     for (int j = 0; j < str!.length; j += _segmentLimit) {
-      final String segment = str.length >= _segmentLimit
-          ? str.substring(j, min(j + _segmentLimit, str.length))
-          : str;
+      final String segment =
+          str.length >= _segmentLimit ? str.slice(j, j + _segmentLimit) : str;
 
       for (int i = 0; i < segment.length; ++i) {
         int c = segment.codeUnitAt(i);

test/unit/extensions/extensions_test.dart

@@ -20,4 +20,15 @@ void main() {
       expect(result, [1, 2, 4, 5]);
     });
   });
+
+  group('StringExtensions', () {
+    test('slice', () {
+      const String str = 'The quick brown fox jumps over the lazy dog.';
+      expect(str.slice(31), 'the lazy dog.');
+      expect(str.slice(31, 1999), 'the lazy dog.');
+      expect(str.slice(4, 19), 'quick brown fox');
+      expect(str.slice(-4), 'dog.');
+      expect(str.slice(-9, -5), 'lazy');
+    });
+  });
 }