Support Nullish coalescing operator ("??") (#67)

It's Stage 3 and already supported in TypeScript 3.7

src/defaults.js

@@ -43,5 +43,6 @@ export const BABEL_PARSING_OPTS = {
     'functionSent',
     'dynamicImport',
     'optionalChaining',
+    'nullishCoalescingOperator',
   ],
 }

tests/fixtures/NullishCoalescing.js

@@ -0,0 +1,10 @@
+import { gettext } from 'gettext-lib'
+
+const someObject = {}
+
+const OptionalChaining = () => {
+  const expressionUsingOptionalChaining = someObject.something ?? 'defaultValue'
+  gettext('Nullish coalescing works')
+}
+
+export default OptionalChaining

tests/tests.js

@@ -527,4 +527,13 @@ describe('react-gettext-parser', () => {
       expect(messages[0].msgid).to.equal('Optional chaining works')
     })
   })
+
+  describe('nullish coalescing support', () => {
+    it('should parse javascript that contains nullish coalescing operator', () => {
+      const code = getSource('NullishCoalescing.js')
+      const messages = extractMessages(code)
+      expect(messages).to.have.length(1)
+      expect(messages[0].msgid).to.equal('Nullish coalescing works')
+    })
+  })
 })