[FIX] negative indices and out of range bugs.

README.md

@@ -42,7 +42,7 @@ Notes about the notation:
 * 	Both `start` and `stop` can be negative, in which case they specify the number of indices from the __maximum__ `array` index.
 
 ``` javascript
-var arr = indexspace( '[:-3]', 5 );
+var arr = indexspace( '[:-2]', 5 );
 // returns [ 0, 1 ]
 ```
 
@@ -104,14 +104,17 @@ arr = indexspace( '[2::2]', 5 );
 arr =  indexspace( '[:10:3]', 20 );
 // returns [ 0, 3, 6, 9 ]
 
+arr = indexspace( '[:-2]', 5 );
+// returns [ 0, 1 ]
+
 arr = indexspace( '[:-1:2]', 5 );
 // returns [ 0, 2 ]
 
 arr = indexspace( '[-4:-1:2]', 5 );
 // returns [ 0, 2 ]
 
 arr = indexspace( '[-5:-1]', 5 );
-// returns [ 0, 1, 2, 3 ]
+// returns [ 0, 1, 2 ]
 
 arr = indexspace( '[::-1]', 5 );
 // returns [ 4, 3, 2, 1, 0 ]

examples/index.js

@@ -37,6 +37,11 @@ console.log( '\n[:10:3]' );
 console.log( arr );
 // returns [ 0, 3, 6, 9 ]
 
+arr = indexspace( '[:-2]', 5 );
+console.log( '\n[:-2]' );
+console.log( arr );
+// returns [ 0, 1 ]
+
 arr = indexspace( '[:-1:2]', 5 );
 console.log( '\n[:-1:2]' );
 console.log( arr );
@@ -50,7 +55,7 @@ console.log( arr );
 arr = indexspace( '[-5:-1]', 5 );
 console.log( '\n[-5:-1]' );
 console.log( arr );
-// returns [ 0, 1, 2, 3 ]
+// returns [ 0, 1, 2 ]
 
 arr = indexspace( '[::-1]', 5 );
 console.log( '\n[::-1]' );

lib/index.js

@@ -219,11 +219,12 @@ function indexspace( str, len ) {
 		}
 		// Handle negative index...
 		else if ( x2 < 0 ) {
-			x2 = len - 1 + x2; // len-1-x2 = (end)-x2
+			x2 = len - 2 + x2; // len-1-x2 = (end)-x2
 			if ( x2 < 0 ) {
 				// WARNING: forgive the user for exceeding index bounds...
 				x2 = 0;
-			} else if ( x2 === x1 ) {
+			}
+			if ( x2 === x1 ) {
 				return [];
 			}
 		}

test/test.js

@@ -92,95 +92,103 @@ describe( 'compute-indexspace', function tests() {
 
 		actual = indexspace( '[:]', 5 );
 		expected = [ 0, 1, 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:]' );
 
 		actual = indexspace( '[2:]', 5 );
 		expected = [ 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[2:]' );
 
 		actual = indexspace( '[:3]', 5 );
 		expected = [ 0, 1, 2 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:3]' );
 
 		actual = indexspace( '[2:4]', 5 );
 		expected = [ 2, 3 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[2:4]' );
 
 		actual = indexspace( '[1:4:2]', 5 );
 		expected = [ 1, 3 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[1:4:2]' );
 
 		actual = indexspace( '[2::2]', 5 );
 		expected = [ 2, 4 ];
 		assert.deepEqual( actual, expected );
 
 		actual =  indexspace( '[:10:3]', 20 );
 		expected = [ 0, 3, 6, 9 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[2::2]' );
+
+		actual = indexspace( '[:-1]', 5 );
+		expected = [ 0, 1, 2 ];
+		assert.deepEqual( actual, expected, '[:-1]' );
+
+		actual = indexspace( '[:-2]', 5 );
+		expected = [ 0, 1 ];
+		assert.deepEqual( actual, expected, '[:-2]' );
 
 		actual = indexspace( '[:-1:2]', 5 );
 		expected = [ 0, 2 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:-1:2]' );
 
 		actual = indexspace( '[-4:-1:2]', 5 );
 		expected = [ 0, 2 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[-4:-1:2]' );
 
 		actual = indexspace( '[-5:-1]', 5 );
-		expected = [ 0, 1, 2, 3 ];
-		assert.deepEqual( actual, expected );
+		expected = [ 0, 1, 2 ];
+		assert.deepEqual( actual, expected, '[-5:-1]' );
 
 		actual = indexspace( '[::-1]', 5 );
 		expected = [ 4, 3, 2, 1, 0 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[::-1]' );
 
 		actual = indexspace( '[:0:-1]', 5 );
 		expected = [ 4, 3, 2, 1 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:0:-1]' );
 
 		actual = indexspace( '[3:0:-1]', 5 );
 		expected = [ 3, 2, 1 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[3:0:-1]' );
 
 		actual = indexspace( '[-1:-4:-2]', 5 );
 		expected = [ 3, 1 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[-1:-4:-2]' );
 	});
 
 	it( 'should support an `end` keyword', function test() {
 		var actual, expected;
 
 		actual = indexspace( '[:end]', 5 );
 		expected = [ 0, 1, 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:end]' );
 
 		actual = indexspace( '[end::-1]', 5 );
 		expected = [ 4, 3, 2, 1, 0 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[end::-1]' );
 
 		actual = indexspace( '[:end-1]', 5 );
 		expected = [ 0, 1, 2, 3 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:end-1]' );
 
 		actual = indexspace( '[:end/2]', 5 );
 		expected = [ 0, 1 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:end/2]' );
 
 		actual = indexspace( '[:end/2]', 6 );
 		expected = [ 0, 1, 2 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:end/2]' );
 
 		actual = indexspace( '[end-2::-1]', 5 );
 		expected = [ 2, 1, 0 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[end-2::-1]' );
 
 		actual = indexspace( '[end/2:]', 5 );
 		expected = [ 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[end/2:]' );
 
 		actual = indexspace( '[end/2:]', 6 );
 		expected = [ 3, 4, 5 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[end/2:]' );
 	});
 
 	it( 'should return an empty array if provided a reference array length equal to 0', function test() {
@@ -192,13 +200,13 @@ describe( 'compute-indexspace', function tests() {
 		var actual;
 
 		actual = indexspace( '[2:end-2]', 5 );
-		assert.deepEqual( actual, [] );
+		assert.deepEqual( actual, [], '[2:end-2]' );
 
 		actual = indexspace( '[2:-2]', 5 );
-		assert.deepEqual( actual, [] );
+		assert.deepEqual( actual, [], '[2:-2]' );
 
 		actual = indexspace( '[2:2]', 5 );
-		assert.deepEqual( actual, [] );
+		assert.deepEqual( actual, [], '[2:2]' );
 	});
 
 	it( 'should return an empty array if start is greater than the end for a positive increment', function test() {
@@ -212,32 +220,44 @@ describe( 'compute-indexspace', function tests() {
 	});
 
 	it( 'should return an empty array if start index is greater than maximum index', function test() {
-		var actual = indexspace( '[5:]', 5 );
-		assert.deepEqual( actual, [] );
+		var actual;
+
+		actual = indexspace( '[5:]', 5 );
+		assert.deepEqual( actual, [], '[5:]' );
+
+		actual = indexspace( '[20:25]', 5 );
+		assert.deepEqual( actual, [], '[20:25]' );
+	});
+
+	it( 'should return an empty array if both indices are less than 0', function test() {
+		var actual;
+
+		actual = indexspace( '[-25:-20]', 5 );
+		assert.deepEqual( actual, [], '[-25:-20]' );
 	});
 
 	it( 'should be forgiving if the user exceeds index bounds', function test() {
 		var actual, expected;
 
 		actual = indexspace( '[-10:]', 5 );
 		expected = [ 0, 1, 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[-10:]' );
 
 		actual = indexspace( '[:10]', 5 );
 		expected = [ 0, 1, 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:10]' );
 
 		actual = indexspace( '[:-10:-1]', 5 );
 		expected = [ 4, 3, 2, 1, 0 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:-10:-1]' );
 
 		actual = indexspace( '[end-10:]', 5 );
 		expected = [ 0, 1, 2, 3, 4 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[end-10:]' );
 
 		actual = indexspace( '[:end-10:-1]', 5 );
 		expected = [ 4, 3, 2, 1, 0 ];
-		assert.deepEqual( actual, expected );
+		assert.deepEqual( actual, expected, '[:end-10:-1]' );
 	});
 
 });