Change to return undefined for out-of-bound offsets

lib/index.js

@@ -32,8 +32,8 @@
  *   Get the `offset` from a line/column based `Point` in the bound indices.
  * @param {PointLike | null | undefined} [point]
  *   Something that should be a `point.
- * @returns {number}
- *   Offset or `-1` for invalid or out of bounds input.
+ * @returns {number | undefined}
+ *   Offset (`number`) or `undefined` for invalid or out of bounds input.
  *
  * @typedef Location
  *   Accessors for index.
@@ -117,7 +117,5 @@ export function location(file) {
         return offset
       }
     }
-
-    return -1
   }
 }

readme.md

@@ -100,7 +100,7 @@ Accessors for index (TypeScript type).
 *   `toPoint` (`(offset: number) => Point | undefined`)
     — get the line/column based [`Point`][point] for `offset` in the bound
     indices
-*   `toOffset` (`(point: Point) => number`)
+*   `toOffset` (`(point: Point) => number | undefined`)
     — get the `offset` from a line/column based [`Point`][point] in the bound
     indices
 

test.js

@@ -44,14 +44,14 @@ test('toOffset(point)', function () {
 
   assert.equal(
     place.toOffset({line: undefined, column: undefined}),
-    -1,
-    'should return `-1` for invalid input'
+    undefined,
+    'should return `undefined` for invalid input'
   )
 
   assert.equal(
     place.toOffset({line: 4, column: 2}),
-    -1,
-    'should return `-1` for out of bounds input'
+    undefined,
+    'should return `undefined` for out of bounds input'
   )
 
   assert.equal(
@@ -71,6 +71,12 @@ test('toOffset(point)', function () {
     11,
     'should return an offset (#3)'
   )
+
+  assert.equal(
+    location('').toOffset({line: 1, column: 1}),
+    0,
+    'should support empty document'
+  )
 })
 
 test('toPoint(offset)', function () {
@@ -99,6 +105,12 @@ test('toPoint(offset)', function () {
     {line: 3, column: 4, offset: 11},
     'should return a point (#2)'
   )
+
+  assert.deepEqual(
+    location('').toPoint(0),
+    {line: 1, column: 1, offset: 0},
+    'should support empty document'
+  )
 })
 
 test('other tests', function () {
@@ -116,7 +128,7 @@ test('other tests', function () {
       place.toOffset({line: 2, column: 1}),
       place.toOffset({line: 2, column: 2})
     ],
-    [3, -1, -1],
+    [3, undefined, undefined],
     'should return offsets for points around an EOF w/o EOLs'
   )
 
@@ -138,7 +150,7 @@ test('other tests', function () {
       place.toOffset({line: 2, column: 1}),
       place.toOffset({line: 2, column: 2})
     ],
-    [3, 4, -1],
+    [3, 4, undefined],
     'should return offsets for points around an EOF EOL'
   )