fix: Use gts to Target Newer Versions of JavaScript

src/pack-n-test.ts

@@ -48,6 +48,10 @@ export interface CodeSample {
 interface TestOptions {
   sample: CodeSample;
   packageDir?: string;
+  /**
+   * Path to a `tsconfig.json` file
+   */
+  tsconfigPath?: string;
 }
 
 interface Sample {
@@ -96,13 +100,18 @@ export async function pack(
   return packageTarball;
 }
 
+/**
+ * `gts`'s `tsconfig.json`.
+ */
+const GTS_CONFIG_PATH = './node_modules/gts/tsconfig-google.json';
+
 export async function packNTest(options: TestOptions) {
   const moduleUnderTest = options.packageDir || process.cwd();
   const installDir = tmp.dirSync().name;
 
   try {
     const tarball = await pack(moduleUnderTest, installDir);
-    await prepareTarget(tarball, options.sample);
+    await prepareTarget(tarball);
     const filename = getExecFilename(options.sample);
     await execa('node', [filename], {cwd: installDir});
   } catch (err) {
@@ -113,15 +122,22 @@ export async function packNTest(options: TestOptions) {
   }
   return;
 
-  async function prepareTarget(tarball: string, sample: CodeSample) {
+  async function prepareTarget(tarball: string) {
     // Generate a package.json.
     await execa('npm', ['init', '-y'], {cwd: installDir});
+    const sample = options.sample;
+    const tsconfigPath = options.tsconfigPath || GTS_CONFIG_PATH;
 
     const dependencies = sample.dependencies || [];
     const devDependencies = sample.devDependencies || [];
 
     if (sample.ts) {
       devDependencies.push('typescript');
+      devDependencies.push('@types/node');
+
+      if (tsconfigPath === GTS_CONFIG_PATH) {
+        devDependencies.push('gts');
+      }
     }
 
     // Add dependencies, including tarball, to package.json.
@@ -138,15 +154,27 @@ export async function packNTest(options: TestOptions) {
       {cwd: installDir}
     );
 
-    // Poupulate test code.
+    // Populate test code.
     const {code, filename} = getSample(sample);
     await writeFile(path.join(installDir, filename), code, 'utf-8');
 
     if (sample.ts) {
-      // TODO: maybe make it flexible for users to pass in typescript config.
-      await execa('npx', ['tsc', '--strict', 'index.ts'], {
-        cwd: installDir,
-      });
+      const testConfig = {
+        extends: tsconfigPath,
+        files: ['index.ts'],
+        compilerOptions: {
+          rootDir: '.',
+          resolveJsonModule: true,
+        },
+      };
+
+      // this is the config `tsc` will use for compilation locally.
+      await writeFile(
+        path.join(installDir, 'tsconfig.json'),
+        JSON.stringify(testConfig)
+      );
+
+      await execa('npx', ['tsc'], {cwd: installDir});
     }
   }
 }

test/fixtures/pass/test/test.ts

@@ -22,6 +22,16 @@ describe('passing tests', () => {
         description: 'basic passing sample',
         ts: `
           import {doStuff} from 'pass';
+
+          export class Example {
+            // ES 2015+ feature
+            #value = 0;
+
+            getValue () {
+              return this.#value;
+            }
+          }
+
           doStuff().then(console.log);
         `,
       },