数字转成字母

发现一个有小坑的题目 Integer to English Words
题目要求：

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

Example 1:
Input: 123
Output: "One Hundred Twenty Three"

Example 2:
Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:
Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Example 4:
Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

就是把一串数字按照英语语法格式输出成字符串的形式。英语不同于汉语，是3个一断。

汉语和英语数字表达的方式不同。汉语是个，十，百，千，万，十万，百万，千万，亿，十亿……，也就是以“十”的倍数来表示；而英语则是在数字超过千以后，以“千”(thousand)的倍数来表达的。如“一万”是“十千”，即 ten thousand；“十万”是“百千”，即 hundred thousand，直至“百万”，million。百万以上的数字则用“百万”的倍数表达；如“千万”是“十百万”，即 ten million；“亿”是“百百万”，即 hundred million，直至“十亿”，billion。 所以英文表达数字时可以从右往左，三位一逗号，逗号从右往左分别对应的是：thousand, million, billion, etc。

@沪江英语www.hjenglish.com/new/p110563

所以程序并不难想，思路也没有那么难，写完之后，一提交发现坑了，丫的最后面不能有空格，改了半天，最后实现了功能，发现代码很长，最后用了自带的函数trim，来去掉了多余的空格，代码也就将就算是自己能看过眼吧。
下面是丑代码

/**
 * @param {number} num
 * @return {string}
 */
var numberToWords = function(num) {
  //debugger
  if(num === 0) return 'Zero'
  let cous = ""
  let index = 0
  let a = [""," One", " Two", " Three", " Four", " Five", " Six", " Seven", " Eight"," Nine", " Ten", " Eleven", " Twelve", " Thirteen", " Fourteen", " Fifteen", " Sixteen", " Seventeen", " Eighteen", " Nineteen"]
  let b = ["",""," Twenty", " Thirty", " Forty", " Fifty", " Sixty", " Seventy", " Eighty", " Ninety"]
  let c = [""," Thousand", " Million", " Billion"]
  let thereword = function (numb) {
    if (numb === 0) return "" 
    let num_temp = ""
   // debugger
    if(numb > 99){
      if(numb % 100 > 19) { 
        num_temp = a[parseInt(numb / 100)] + " Hundred" + b[parseInt((numb % 100) / 10)] + a[parseInt((numb % 100) % 10)]
      } else {
        num_temp = a[parseInt(numb / 100)] + " Hundred" + a[numb % 100] 
      }
    } else {
      if(numb > 19) {
        num_temp = b[parseInt(numb / 10)] + a[numb % 10]
      } else {
        num_temp = a[numb]
      }
    }
    return num_temp
    }   
    while(num > 0) {
    let nums = thereword(num % 1000)
    if(nums !== "") {
       cous =  nums + c[index] + cous
    } else {
       cous =  nums + cous
    }      
    num = (num - num % 1000) / 1000   
    index++
    }
    return cous.trim()
};

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以后需要注意更多的细节要求