ES6 new features arrow function and commonly used function () comparison

// 无 参
var fn1 = function () {}
 var fn1 = () => {}
 
// Single parameter 
var fn2 = function (a) {}
 var fn2 = a => {}
 
// Multiple parameters 
var fn3 = function (a, b) {}
 var fn3 = (a, b) => {}
 
// Variable parameters 
var fn4 = function (a, b, ... args) {}
 var fn4 = (a, b, ... args) => {}