separatePinyinInSyllables.js

var separatePinyinInSyllables = function (pinyin) {

  var vowels = 'aāáǎàeēéěèiīíǐìoōóǒòuūúǔù';

  return pinyin
            .replace(new RegExp('([' + vowels + '])([^' + vowels + 'nr\w\s])'), '$1 $2') // This line does most of the work
            .replace(new RegExp('(\w)([csz]h)'), '$1 $2') // double-consonant initials
            .replace(new RegExp('(n)([^' + vowels + 'vg\w\s])'), '$1 $2') // cleans up most n compounds
            .replace(new RegExp('([' + vowels + 'v])([^' + vowels + '\w\s])([' + vowels + 'v])'), '$1 $2$3') // assumes correct Pinyin (i.e., no missing apostrophes)
            .replace(new RegExp('([' + vowels + 'v])(n)(g)([' + vowels + 'v])'), '$1$2 $3$4') // assumes correct Pinyin, i.e. changan = chan + gan
            .replace(new RegExp('([gr])([^' + vowels + '])'), '$1 $2') // fixes -ng and -r finals not followed by vowels
            .replace(new RegExp('([^e\w\s])(r)'), '$1 $2'); // r an initial, except in er
  
};