ES6 生成器函数

"use strict"
function* rainbow() {
   // the asterisk marks this as a generator
   yield 'red';
   yield 'orange';
   yield 'yellow';
   yield 'green';
   yield 'blue';
   yield 'indigo';
   yield 'violet';
}
for(let color of rainbow()) {
   console.log(color);
}