Tests for ES6 arrow function, make sure parsing is OK in strict mode. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS f1(10) is 10 PASS f2(20) is 20 PASS f3(10, 20) is 30 PASS f4(20, 20) is 40 PASS foo(x => x + 1) is 11 PASS foo((x) => x + 1) is 11 PASS foo(x => { return x + 1; }) is 11 PASS foo((x) => { return x + 1; }) is 11 PASS successfullyParsed is true TEST COMPLETE