feat(utils): allow dateparts without day specified (#16)

Author: ships

src/utils.ts

@@ -85,16 +85,20 @@ export function DateZFromDateParts(d: DateParts, opts: DateParseOpts = DefaultOp
     throw new Error('Malformed DateParts: Multiple DateParts possibilities found')
   }
 
+  // choose the first dateparts in the list.
+  // TODO this is opinionated behavior and may need to adapt.
   const best = p[0]
-  if (best.length != 3) {
-    throw new Error('Malformed DateParts: Must have exactly year, month, and day')
-  }
-
-  const yr = best[0]
-  const moIdx = best[1] - 1
-  const day = best[2]
 
-  return new Date(Date.UTC(yr, moIdx, day))
+  switch (best.length) {
+    case 1:
+      return new Date(Date.UTC(best[0], 0, 1))
+    case 2:
+      return new Date(Date.UTC(best[0], best[1] - 1, 1))
+    case 3:
+      return new Date(Date.UTC(best[0], best[1] - 1, best[2]))
+    default:
+      throw new Error('Malformed DateParts: Must have 1, 2, or 3 parts')
+  }
 }
 
 /**

test/unit/utils.test.ts

@@ -19,6 +19,13 @@ test('date utilities: DateParts only', async (t) => {
   t.is(result, '2021-01-21T00:00:00.000Z')
 })
 
+test('date utilities: DateParts only with only year and month', async (t) => {
+  const result = U.DatemorphISOString({
+    'date-parts': [CONSISTENT_DATE['date-parts'][0].slice(0, 1)],
+  })
+  t.is(result, '2021-01-01T00:00:00.000Z')
+})
+
 test('date utilities: Inconsistent date, strict', async (t) => {
   t.throws(() => {
     U.DatemorphISOString(INCONSISTENT_DATE)