JS编程实现简单模板引擎变量替换

最近看了一道题：

JS编码实现一个render方法，使得可议这样调用： 
const year = ‘2017’; 
const month = ‘09’; 
const day = ‘21’; 
const str = render(‘year−year−{month}-${day}’)({year,month,day}); 
console.log(str)//输出2017-09-21

我简单的实现了一下：

render (str) {
      return function (obj) {
        str = str.replace('year', obj.year)
        str = str.replace('(month)', obj.month)
        str = str.replace('$(day)', obj.day)
        return str
      }
    },
    tranform () {
      const year = '2018'
      const month = '9'
      const day = '21'
      const str = this.render('year-(month)-$(day)')({ year, month, day })
      console.log(str)
    },