无法弄清楚为什么我得到“无法读取未定义的属性'0'”错误

Question

I'm trying to do the Roman Numeral challenge from freeCodeCamp. I have no idea why I'm getting the following error:

if(numKey[i][0] <= remaining) { TypeError: Cannot read property '0' of undefined`

Here's my code:

function convertToRoman(num) {
 const numKey = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'], [100, 'C'], [90, 'XC'], [50,'L'], [40, 'XL'],  [10, 'X'], [9, 'IX'] [5, 'V'], [4, 'IV'] [1, 'I']];
 let remaining = num;
 let romanStr = '';
 while(remaining > 0) {
      for(let i = 0; i < numKey.length; i++) {
            if(numKey[i][0] <= remaining) {
                  let j = 0;
                  while(j < Math.floor(remaining/numKey[i][0])) {
                        romanStr += numKey[i][1]
                        remaining -= numKey[i][0] * Math.floor(remaining/numKey[i][0])
                        j++
                  }
            }
      }
      break;
 }
 return romanStr;
}

I have no idea why numKey[i][0] would be undefined. As far as I know it is never out of range, and when I do console.log(numKey[i][0]) in the line above, it always prints the correct value. Is there something I am missing?

Thanks!

Answer 1

You loop is correct .but array is wrong missing some , in last two arrays

[9, 'IX'] [5, 'V'], [4, 'IV'] [1, 'I'] is are invalid one

Check this below snippet. See its undefined one

 const numKey = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'], [100, 'C'], [90, 'XC'], [50,'L'], [40, 'XL'], [10, 'X'], [9, 'IX'] [5, 'V'], [4, 'IV'] [1, 'I']]; console.log(numKey) 

 function convertToRoman(num) { const numKey = [ [1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'], [100, 'C'], [90, 'XC'], [50, 'L'], [40, 'XL'], [10, 'X'], [9, 'IX'],[5, 'V'], [4, 'IV'],[1, 'I'] ]; let remaining = num; let romanStr = ''; while (remaining > 0) { for (let i = 0; i < numKey.length; i++) { if (numKey[i][0] <= remaining) { let j = 0; while (j < Math.floor(remaining / numKey[i][0])) { romanStr += numKey[i][1] remaining -= numKey[i][0] * Math.floor(remaining / numKey[i][0]) j++ } } } break; } return romanStr; } console.log(convertToRoman(5)) 

Answer 2

I think you just have a typo in your code, the numKey array was just not correctly formatted:

Try:

 function convertToRoman(num) { const numKey = [[1000, 'M'], [900, 'CM'], [500, 'D'], [400, 'CD'], [100, 'C'], [90, 'XC'], [50,'L'], [40, 'XL'], [10, 'X'], [9, 'IX'], [5, 'V'], [4, 'IV'], [1, 'I']]; let remaining = num; let romanStr = ''; while(remaining > 0) { for(let i = 0; i < numKey.length; i++) { if(numKey[i][0] <= remaining) { let j = 0; while(j < Math.floor(remaining/numKey[i][0])) { romanStr += numKey[i][1] remaining -= numKey[i][0] * Math.floor(remaining/numKey[i][0]) j++ } } } break; } return romanStr; } console.log(convertToRoman(133)); console.log(convertToRoman(42));