解析辅助类字符串：Now Time ${time}

renderString.js

function renderParser(string,data){
  const S_CODE = 0x24 // start CODE $
  const S_LEFT = 0x7b // {
  const S_RIGHT = 0x7d  // }
  const S_SPACE = 0x20
  let length = string.length
  let at = 0,code,expession = '',expessionResult = ''
  let isEnterExpression = false
  let result = ''
  function charAt(at){
    if(at < 0 || at >= length){
      return false
    }
    return string[at].charCodeAt()
  }
  // 解析表达式，可以考虑解析 +-*/等等
  function parseExpression(expession){
    return expession.split('.').reduce((val,key) => {
      val = val[key] || ''
      if(typeof val === 'function'){
        val = val.call(data)
      }
      return val
    },data)
  }

  while(at < length){
    code = charAt(at)
    if(code === S_CODE && charAt(at + 1) === S_LEFT){ // 下一个字符必须为{
      isEnterExpression = true
    }else if(isEnterExpression && code === S_RIGHT){ // 结束
      expessionResult = parseExpression(expession)
      expession = ''
      isEnterExpression = false
      result += expessionResult
    }else{
      if(isEnterExpression){
        // 忽略首位和空格
        if(code !== S_SPACE && code !== S_LEFT){
          expession += string[at]
        }
      }else{
        result += string[at]
      }
    }
    at++
  }
  return result
}

String.prototype.render = function(data){
  return renderParser(this,data)
}


var greeting = 'Now Time ${time} My name is ${ name },fullName is ${fullName}, age ${age }, I am a ${job.jobName}， deep value ${ job.deep.value }';
var employee = {
    firstName:'Tom',
    name: 'XiaoMing',
    age: 11,
    job: {
        jobName: 'designer',
        jobLevel: 'senior',
        deep:{
          value:'deep_value'
        }
    },
    fullName:function(){
      return this.firstName + ' ' + this.name
    },
    time:function(){
      return Date.now()
    }
};
var result = greeting.render(employee);