Add additional TypeScript tests

tasks/local-test.sh

@@ -8,7 +8,7 @@ function print_help {
   echo "Usage: ${0} [OPTIONS]"
   echo ""
   echo "OPTIONS:"
-  echo "  --node-version <version>  the node version to use while testing [8]"
+  echo "  --node-version <version>  the node version to use while testing [12]"
   echo "  --git-branch <branch>     the git branch to checkout for testing [the current one]"
   echo "  --test-suite <suite>      which test suite to use ('simple', installs', 'kitchensink', 'kitchensink-eject', 'all') ['all']"
   echo "  --interactive             gain a bash shell after the test run"
@@ -18,7 +18,7 @@ function print_help {
 
 cd $(dirname $0)
 
-node_version=8
+node_version=12
 current_git_branch=`git rev-parse --abbrev-ref HEAD`
 git_branch=${current_git_branch}
 test_suite=all

test/fixtures/typescript-advanced/src/App.tsx

@@ -6,11 +6,20 @@ interface MyType {
   baz?: { n: number };
 }
 
+function assertIsString(val: any): asserts val is string {
+  if (typeof val !== "string") {
+      throw new Error("Not a string!");
+  }
+}
+
+const foo: any = "bar";
+assertIsString(foo);
+
 type MyObject = Pick<MyType, 'bar' | 'baz'>;
 
 class App extends React.Component {
   static foo: MyObject = { bar: true, baz: { n: 123 } };
-  n = App.foo.baz!.n;
+  n = App.foo?.baz!.n ?? "foo";
 
   render() {
     return <div />;