Tests for ES6 arrow function toString() method On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". var simpleArrowFunction = () => {} PASS simpleArrowFunction.toString() is '() => {}' PASS ((x) => { x + 1 }).toString() is '(x) => { x + 1 }' PASS (x => x + 1).toString() is 'x => x + 1' var f0 = x => x PASS f0.toString() is 'x => x' var f1 = () => this PASS f1.toString() is '() => this' var f2 = x => { return x; }; PASS f2.toString() is '(x) => { return x; }' var f3 = (x, y) => { return x + y; }; PASS f3.toString() is '(x, y) => { return x + y; }' function foo(x) { return x.toString()}; PASS foo((x)=>x) is '(x)=>x' var a = z => z*2, b = () => ({}); PASS a.toString() is 'z => z*2' PASS b.toString() is '() => ({})' var arrExpr = [y=>y + 1, x=>x]; PASS arrExpr[0].toString() is 'y=>y + 1' PASS arrExpr[1].toString() is 'x=>x' var arrBody = [y=>{ y + 1 }, x=>{ x }]; PASS arrBody[0].toString() is 'y=>{ y + 1 }' PASS arrBody[1].toString() is 'x=>{ x }' PASS successfullyParsed is true TEST COMPLETE