1.模拟next方法返回值的例子

function makeIterator(array){   var nextIndex = 0;   return {     next: function(){       return nextIndex < array.length ? {value: array[nextIndex++],done:false} : {value: undefined, done: true};     }   }}var it = makeIterator(['a','b']);it.next(); // {value: "a", done: false}it.next(); // {value: "b", done: true}it.next(); // {value: undefined, done: true}