Handle TSNonNullExpression and test it

__tests__/src/getPropValue-test.js

@@ -1,7 +1,7 @@
 /* eslint-env mocha */
 /* eslint no-template-curly-in-string: 0 */
 import assert from 'assert';
-import { extractProp } from '../helper';
+import { extractProp, changePlugins } from '../helper';
 import getPropValue from '../../src/getPropValue';
 
 describe('getPropValue', () => {
@@ -111,6 +111,16 @@ describe('getPropValue', () => {
       assert.equal(expected, actual);
     });
 
+    it('should work with a Typescript non-null assertion', () => {
+      changePlugins(pls => [...pls, 'typescript']);
+      const prop = extractProp('<div foo={bar!} />');
+
+      const expected = 'bar';
+      const actual = getPropValue(prop);
+
+      assert.equal(expected, actual);
+    });
+
     it('should return undefined when identifier is literally `undefined`', () => {
       const prop = extractProp('<div foo={undefined} />');
 

src/values/expressions/index.js

@@ -107,7 +107,12 @@ export default function extract(value) {
   } else {
     expression = value;
   }
-  const { type } = expression;
+  let { type } = expression;
+
+  if (type === 'TSNonNullExpression') {
+    expression = expression.expression;
+    type = expression.type;
+  }
 
   if (TYPES[type] === undefined) {
     throw new Error(errorMessage(type));