[8kyu]How old will I be in 2099?

该算法题来自于 codewars【语言: javascript】，翻译如有误差，敬请谅解~

• 场景

Philip 刚刚四岁，他想知道他将来在未来几年多少岁，比如2090年或3044年。他的父母无法跟上计算，所以他们请求你帮助他们写一个程序，可以回答 Philip 无休止的问题。

• 任务

  • 写一个函数，它会有两个参数：出生年份和想要计算的年数。由于 Philip 每天都乐忠于玩这个游戏，他很快就想知道他还有多久出生，所以你的函数需要计算未来和过去两个时期。

  • 提供以下格式的输出：
    1. 对于未来的日期：“You are ... year(s) old.”。
    2. 对于过去的日期：“You will be born in ... year(s).”。
    3. 如果出生年份等于要求计算的日期：“You were born this very year!”
  • “...”将由​​数字代替。请注意，您需要区别 “year” 和 “years” ，这个取决于计算出来的结果。

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• 解答
• 其一

const calculateAge = (birth, year) => {  
      const result = year - birth;
      let old = '';
      if (result > 0){
        old = "You are " + (result > 1 ? result + " years old." : result + " year old.")
      } else {
        if(!!result){
          old = "You will be born in "+ (-result > 1 ? -result + " years." : -result + " year." )
        } else {
          old = "You were born this very year!";  
        }
      }
      return old;
}

• 其二

function  calculateAge(m, n) {
      if(m == n) return 'You were born this very year!';
      var year = Math.abs(m-n) == 1 ? 'year' : 'years';
      if(m < n) return "You are "+(n-m)+' '+year+' old.';
      if(m > n) return "You will be born in "+(-n+m)+' '+year+'.';
}

• 其三

var  calculateAge = (b,c) => {
      r = c-b;
      switch(true) {
        case (r>1):     return "You are " + r + " years old."; break;
        case (r===1):   return "You are 1 year old."; break;
        case (r===0):   return "You were born this very year!"; break;
        case (r===-1):  return "You will be born in 1 year."; break;
        case (r<-1):    return "You will be born in " + (-r) + " years."; break;
      }
}

• 其四

// es6 模板字符串
function calculateAge(a,b) {
      return   a > b  
         ?  `You will be born in ${a-b} year${a-b==1?"":"s"}.` 
         :  a < b ? `You are ${b-a} year${b-a==1?"":"s"} old.` :  `You were born this very year!`
}

• 其五

const calculateAge = (a, b) => 'You ' + (a == b ? 'were born this very year!' : a > b ? `will be born in ${a - b} year${a - b != 1 ? 's' : ''}.`: `are ${b - a} year${b - a != 1 ? 's' : ''} old.`);

• 其六

function calculateAge(birth, query) {
      const diff = Math.max(...arguments) - Math.min(...arguments);
      const isPlural = diff > 1 ? 's' : '';
      return {
        [birth < query]: `You are ${diff} year${isPlural} old.`,
        [birth > query]: `You will be born in ${diff} year${isPlural}.`,
        [birth === query]: "You were born this very year!"
      }[true]
}