Jupe Parsing.js

var regexps = [
  {
    'regexp': /`([^`]*)`/g,
    'flag': 'code'
  },
  {
    'regexp': /\*\*([^\*]*)\*\*/g,
    'flag': 'bold'
  },
  {
    'regexp': /\*([^\*]*)\*/g,
    'flag': 'em'
  },
  {
    'regexp': /_([^_]*)_/g,
    'flag': 'underline'
  },
  {
    'regexp': /#(\d*[a-zA-Z_]+)/g,
    'flag': 'channel'
  },
];

function parse(str) {
  var charmap = str.split('').map(function(e, i) {
    return {
      character: e,
      flags: []
    };
  });

  regexps.forEach(function(regexp, i) {
    var matches = str.match(regexp.regexp);
    if (matches !== null) {
      matches.forEach(function(match, i) {
        var matchIndex = str.indexOf(match);
        charmap[matchIndex].flags.push('initial');
        charmap[(matchIndex + match.length) - 1].flags.push('terminal');

        for(var charIndex = matchIndex; charIndex < (matchIndex + match.length); charIndex++) {
          charmap[charIndex].flags.push(regexp.flag);
        }
      });
    }
  });

  console.log(charmap);

}

parse('`this` is a *_test_* this is a #channel');

/*
 ***** OUTPUT *****
 
[ { character: '`', flags: [ 'initial', 'code' ] },
  { character: 't', flags: [ 'code' ] },
  { character: 'h', flags: [ 'code' ] },
  { character: 'i', flags: [ 'code' ] },
  { character: 's', flags: [ 'code' ] },
  { character: '`', flags: [ 'terminal', 'code' ] },
  { character: ' ', flags: [] },
  { character: 'i', flags: [] },
  { character: 's', flags: [] },
  { character: ' ', flags: [] },
  { character: 'a', flags: [] },
  { character: ' ', flags: [] },
  { character: '*', flags: [ 'initial', 'em' ] },
  { character: '_', flags: [ 'em', 'initial', 'underline' ] },
  { character: 't', flags: [ 'em', 'underline' ] },
  { character: 'e', flags: [ 'em', 'underline' ] },
  { character: 's', flags: [ 'em', 'underline' ] },
  { character: 't', flags: [ 'em', 'underline' ] },
  { character: '_', flags: [ 'em', 'terminal', 'underline' ] },
  { character: '*', flags: [ 'terminal', 'em' ] },
  { character: ' ', flags: [] },
  { character: 't', flags: [] },
  { character: 'h', flags: [] },
  { character: 'i', flags: [] },
  { character: 's', flags: [] },
  { character: ' ', flags: [] },
  { character: 'i', flags: [] },
  { character: 's', flags: [] },
  { character: ' ', flags: [] },
  { character: 'a', flags: [] },
  { character: ' ', flags: [] },
  { character: '#', flags: [ 'initial', 'channel' ] },
  { character: 'c', flags: [ 'channel' ] },
  { character: 'h', flags: [ 'channel' ] },
  { character: 'a', flags: [ 'channel' ] },
  { character: 'n', flags: [ 'channel' ] },
  { character: 'n', flags: [ 'channel' ] },
  { character: 'e', flags: [ 'channel' ] },
  { character: 'l', flags: [ 'terminal', 'channel' ] } ]
 
 */