ES6标准新增了一种新的函数：Arrow Function（箭头函数）。
常规函数定义：
function() {}
箭头函数，在定义函数时，移除了function, return 和{}。
无参数案例：
const queue = ['Dave', 'Sarah', 'Sharon']; const nextCustomer = () => queue[0]; console.log(nextCustomer()); // 'Dave'有参数案例：
var a = [ "We're up all night 'til the sun", "We're up all night to get some", "We're up all night for good fun", "We're up all night to get lucky" ]; // These two assignments are equivalent: // Old-school: var a2 = a.map(function(s){ return s.length }); // ECMAscript 6 using arrow functions var a3 = a.map( s => s.length ); // both a2 and a3 will be equal to [31, 30, 31, 31]
