ES5:function f (a, b) {return a + b;}-->ES6let f = (a, b) => a + bES5:function f (a, b) {console.log('Hello ES6.');return a + b;}-->ES6let f = (a, b) => {console.log('Hello ES6.');return a + b;}如果把函数写在代码块里面,有return需要自己写return。