Remove exception in format (#454)

CHANGELOG.md

@@ -262,24 +262,6 @@ This change log follows the format documented in [Keep a CHANGELOG].
   //=> 1
   ```
 
-- **BREAKING**: now `format` throws an exception if the passed date is `Invalid Date`.
-
-  ```javascript
-  // Before v2.0.0
-  var result = format(date, 'YYYY-MM-DD')
-  if (result === 'Invalid Date') {
-    // ...
-  }
-
-  // v2.0.0 onward
-  try {
-    var result = format(date, 'YYYY-MM-DD')
-    // ...
-  } catch (e) {
-    // ...
-  }
-  ```
-
 - **BREAKING**: `format` now assumes that the provided locale uses UTC-versions of `Date` methods,
   e.g. `getUTCMonth` instead of `getMonth`. All included locales are converted.
   This change affects only those who uses custom locales.

src/format/index.js

@@ -72,7 +72,6 @@ import getUTCISOYear from './_lib/getUTCISOYear/index.js'
  * @param {Options} [options] - the object with options. See [Options]{@link docs/Options}
  * @param {Locale} [options.locale=enLocale] - the locale object. See [Locale]{@link docs/Locale}
  * @returns {String} the formatted date string
- * @throws {Error} The date must be valid
  *
  * @example
  * // Represent 11 February 2014 in middle-endian format:
@@ -110,7 +109,7 @@ export default function format (dirtyDate, dirtyFormatStr, dirtyOptions) {
   var originalDate = toDate(dirtyDate, options)
 
   if (!isValid(originalDate, options)) {
-    throw new Error('Date is invalid')
+    return 'Invalid Date'
   }
 
   // Convert the date in system timezone to the same date in UTC+00:00 timezone.

src/format/test.js

@@ -315,9 +315,8 @@ describe('format', function () {
   })
 
   describe('edge cases', function () {
-    it('throws an exception if the date isn\'t valid', function () {
-      var block = format.bind(null, new Date(NaN), 'MMMM D, YYYY')
-      assert.throws(block)
+    it('returns String(\'Invalid Date\') if the date isn\'t valid', function () {
+      assert(format(new Date(NaN), 'MMMM D, YYYY') === 'Invalid Date')
     })
 
     it('handles dates before 100 AD', function () {