Improve at()

Author: smikitky

api-reference.md

@@ -364,9 +364,9 @@ at(data: MultiIntegerRange, index: number): number | undefined
 |-|-|
 | `data` | The value. |
 | `index` | The 0-based index of the integer to return. Can be negative. |
-| Returns | The N-th integer. Returns `undefined` if the index is out of bounds. |
+| Returns | The integer at the specified index. Returns `undefined` if the index is out of bounds. |
 
-Returns the N-th integer of the given MultiIntegerRange.
+Returns the integer at the specified 0-based index.
 If a negative index is given, the index is counted from the end.
 
 ### Example

src/fp.test.ts

@@ -404,6 +404,9 @@ test('at', () => {
   t('-4,8-10', 6, RangeError);
   t('-4,8-10', -7, 1);
   t('2-4,8-', -7, RangeError);
+
+  t('', Infinity, RangeError);
+  t('', -Infinity, RangeError);
   t('', 0, undefined);
   t('', 1, undefined);
   t('', -1, undefined);

src/fp.ts

@@ -424,11 +424,12 @@ export const max = (data: MIR): number | undefined => {
 };
 
 /**
- * Returns the N-th integer of the given MultiIntegerRange.
+ * Returns the integer at the specified 0-based index.
  * If a negative index is given, the index is counted from the end.
  * @param data - The value.
  * @param index - The 0-based index of the integer to return. Can be negative.
- * @returns The N-th integer. Returns `undefined` if the index is out of bounds.
+ * @returns The integer at the specified index.
+ *   Returns `undefined` if the index is out of bounds.
  * @example
  * at([[2, 4], [8, 10]], 4); // 9
  * at([[2, 4], [8, 10]], 6); // undefined
@@ -438,8 +439,9 @@ export const at = (data: MIR, index: number): number | undefined => {
   if (index === Infinity || index === -Infinity)
     throw new RangeError('at() was invoked with an invalid index');
   if (
-    (index >= 0 && data[0]?.[0] === -Infinity) ||
-    (index < 0 && data[data.length - 1]?.[1] === Infinity)
+    data.length > 0 &&
+    ((index >= 0 && data[0][0] === -Infinity) ||
+      (index < 0 && data[data.length - 1][1] === Infinity))
   ) {
     throw new RangeError('at() was invoked on an unbounded range');
   }