feat(internal): formatList

Signed-off-by: Lexus Drumgold <[email protected]>

Author: unicornware

src/internal/__tests__/format-list.spec.ts

@@ -0,0 +1,22 @@
+/**
+ * @file Unit Tests - formatList
+ * @module create-error-node/internal/tests/unit/formatList
+ */
+
+import testSubject from '../format-list'
+
+describe('unit:internal/formatList', () => {
+  it('should return list string', () => {
+    // Arrange
+    const cases: [...Parameters<typeof testSubject>, string][] = [
+      [['json'], undefined, 'json'],
+      [['data', 'file'], undefined, 'data and file'],
+      [['boolean', 'number', 'string'], 'or', 'boolean, number, or string']
+    ]
+
+    // Act + Expect
+    cases.forEach(([arr, transition, expected]) => {
+      expect(testSubject(arr, transition)).to.equal(expected)
+    })
+  })
+})

src/internal/format-list.ts

@@ -0,0 +1,30 @@
+/**
+ * @file Internal - formatList
+ * @module errnode/internal/formatList
+ * @see https://github.com/nodejs/node/blob/0f69ec4dd74d446765639274728466baf5f13cdd/lib/internal/errors.js#L905-L908
+ */
+
+/**
+ * Creates a list string in the form `'A and B'` or `'A, B, ..., and Z`.
+ *
+ * @example
+ *  formatList(['json'])
+ *  // 'json'
+ * @example
+ *  formatList(['data', 'file'])
+ *  // 'data and file'
+ * @example
+ *  formatList(['boolean', 'number', 'string'], 'or')
+ *  // 'boolean, number, or string'
+ *
+ * @param {string[]} arr - List elements
+ * @param {string?} [transition='and'] - Word to be inserted before last element
+ * @return {string} List string
+ */
+function formatList(arr: string[], transition: string = 'and'): string {
+  return arr.length < 3
+    ? arr.join(` ${transition} `)
+    : `${arr.slice(0, -1).join(', ')}, ${transition} ${arr[arr.length - 1]}`
+}
+
+export default formatList