git.squeep.com Git - squeep-roman/blob - index.js

   1 'use strict';
   2
   3 /**
   4  * Integer to Unicode character.
   5  * These pre-combined numbers are only used for direct digit mappings
   6  * for these numbers.
   7  * A previous implementation would compact occurrences of these multi-character
   8  * combinations in larger numbers; however, some fonts render the multi-character
   9  * combinations as slightly different sizes than the stand-alone characters,
  10  * which made them render oddly.
  11  */
  12 const singleMapping = {
  13   1: '\u2160', // Ⅰ &#8544;
  14   2: '\u2161', // Ⅱ &#8545;
  15   3: '\u2162', // Ⅲ &#8546;
  16   4: '\u2163', // Ⅳ &#8547;
  17   5: '\u2164', // Ⅴ &#8548;
  18   6: '\u2165', // Ⅵ &#8549;
  19   7: '\u2166', // Ⅶ &#8550;
  20   8: '\u2167', // Ⅷ &#8551;
  21   9: '\u2168', // Ⅸ &#8552;
  22   10: '\u2169', // Ⅹ &#8553;
  23   11: '\u216a', // Ⅺ &#8554;
  24   12: '\u216b', // Ⅻ &#8555;
  25 };
  26
  27 /**
  28  * Viable mappings from a number to the Roman representation.
  29  */
  30 const mapping = {
  31   1: '\u2160', // Ⅰ &#8544;
  32   4: '\u2160\u2164', // ⅠⅤ &#8544;&#8548;
  33   5: '\u2164', // Ⅴ &#8548;
  34   9: '\u2160\u2169', // Ⅸ &#8552;
  35   10: '\u2169', // Ⅹ &#8553;
  36   40: '\u2169\u216c', // ⅩⅬ &#8553;&#8556;
  37   50: '\u216c', // Ⅼ &#8556;
  38   90: '\u2169\u216d', // ⅩⅭ &#8553;&#8557;
  39   100: '\u216d', // Ⅽ &#8557;
  40   400: '\u216d\u216e', // ⅭⅮ &#8557;&#8558;
  41   500: '\u216e', // Ⅾ &#8558;
  42   900: '\u216d\u216f', // ⅭⅯ &#8557;&#8559;
  43   1000: '\u216f', // Ⅿ &#8559;
  44 };
  45
  46 /**
  47  * Render all characters of #s as HTML-encoded entities.
  48  * @param {String} s
  49  * @returns {string}
  50  */
  51 function htmlEncode(s) {
  52   return s
  53     .split('')
  54     .map((c) => `&#${c.codePointAt(0)};`)
  55     .join('');
  56 }
  57
  58 /**
  59  * The keys of our number->roman mappings, sorted highest-first.
  60  * We will walk this list, rendering input-value-divided-
  61  * by-the-key-number mapped values, modulus-ing the input-value, and
  62  * repeating for the remaining key-numbers.
  63  */
  64 const divisors = Object.keys(mapping)
  65   .sort((a, b) => b - a)
  66   .map(Number);
  67
  68 /**
  69  * Convert a number to its Roman representation, using Unicode characters
  70  * or HTML entities.
  71  * @param {Number} num
  72  * @param {Boolean} asEntities if true, return html instead of unicode
  73  * @returns {String}
  74  * @throws {RangeError}
  75  */
  76 function toRoman(num, asEntities = false) {
  77   if (!num || isNaN(Number(num))) {
  78     throw new RangeError(`cannot convert '${num}' (${typeof num})`);
  79   }
  80   if (num < 0) {
  81     throw new RangeError('cannot convert negative numbers');
  82   }
  83   const romanDigits = [];
  84   if (num <= 12) {
  85     romanDigits.push(singleMapping[num]);
  86   } else {
  87     divisors.forEach((d) => {
  88       const length = Math.floor(num / d);
  89       romanDigits.push(mapping[d].repeat(length));
  90       num %= d;
  91     });
  92   }
  93   const romanString = romanDigits.join('');
  94
  95   return asEntities ? htmlEncode(romanString) : romanString;
  96 }
  97
  98 module.exports = {
  99   toRoman,
 100 };