fix(page.evaluate): better function serialization

lib/ExecutionContext.js

@@ -94,8 +94,26 @@ class ExecutionContext {
     if (typeof pageFunction !== 'function')
       throw new Error('The following is not a function: ' + pageFunction);
 
+    let functionText = pageFunction.toString();
+    try {
+      new Function('(' + functionText + ')');
+    } catch (e1) {
+      // This means we might have a function shorthand. Try another
+      // time prefixing 'function '.
+      if (functionText.startsWith('async '))
+        functionText = 'async function ' + functionText.substring('async '.length);
+      else
+        functionText = 'function ' + functionText;
+      try {
+        new Function('(' + functionText  + ')');
+      } catch (e2) {
+        // We tried hard to serialize, but there's a weird beast here.
+        throw new Error('Passed function is not well-serializable!');
+      }
+    }
+
     const { exceptionDetails, result: remoteObject } = await this._client.send('Runtime.callFunctionOn', {
-      functionDeclaration: pageFunction.toString() + '\n' + suffix + '\n',
+      functionDeclaration: functionText + '\n' + suffix + '\n',
       executionContextId: this._contextId,
       arguments: args.map(convertArgument.bind(this)),
       returnByValue: false,

test/page.spec.js

@@ -23,6 +23,13 @@ const DeviceDescriptors = utils.requireRoot('DeviceDescriptors');
 const iPhone = DeviceDescriptors['iPhone 6'];
 const iPhoneLandscape = DeviceDescriptors['iPhone 6 landscape'];
 
+let asyncawait = true;
+try {
+  new Function('async function foo() {await 1}');
+} catch (e) {
+  asyncawait = false;
+}
+
 module.exports.addTests = function({testRunner, expect, headless}) {
   const {describe, xdescribe, fdescribe} = testRunner;
   const {it, fit, xit} = testRunner;
@@ -65,12 +72,6 @@ module.exports.addTests = function({testRunner, expect, headless}) {
     });
   });
 
-  let asyncawait = true;
-  try {
-    new Function('async function foo() {await 1}');
-  } catch (e) {
-    asyncawait = false;
-  }
   (asyncawait ? describe : xdescribe)('Async stacks', () => {
     it('should work', async({page, server}) => {
       server.setRoute('/empty.html', (req, res) => {
@@ -176,6 +177,17 @@ module.exports.addTests = function({testRunner, expect, headless}) {
       const result = await page.evaluate(() => 7 * 3);
       expect(result).toBe(21);
     });
+    (asyncawait ? it : xit)('should work with function shorthands', async({page, server}) => {
+      // trick node6 transpiler to not touch our object.
+      // TODO(lushnikov): remove eval once Node6 is dropped.
+      const a = eval(`({
+        sum(a, b) { return a + b; },
+
+        async mult(a, b) { return a * b; }
+      })`);
+      expect(await page.evaluate(a.sum, 1, 2)).toBe(3);
+      expect(await page.evaluate(a.mult, 2, 4)).toBe(8);
+    });
     it('should throw when evaluation triggers reload', async({page, server}) => {
       let error = null;
       await page.evaluate(() => {