Split text into equal length strings keeping words intact

Here's how to fix the original code:

Add the following after line 40:

in_text = false;

The in_text flag is used by the code to determine if the current position is in regular text. However, it was not clearing the flag when it entered a region of formatting markup. This was the cause care of the main issue described in the question with the ultra-short line.

Change the if statement at line 76/77 to:

if (is_space() && ((formatting && in_text) || !formatting || (line[j] === '[' && line[j+1] === '['))) {

This takes care of a lesser problem where line breaks were not happening on spaces between regular text and formatted text.

Working fiddle here: https://jsfiddle.net/2w10xp3m/1/

I think I've solved the problem using a much simpler approach. First break up all words, then re-assemble the lines while keeping track of the current format. See JsFiddle.

JavaScript

$.terminal.split_equal = function(str, length, words) {
  var result = [],
    currentFormat = null,
    currentLine = '',
    currentLineLengthWithoutFormatting = 0;

  // 1. Split words on  
  words = str.split(/ /g);

  // 2. Re-assemble lines while keeping track of current formats
  words.forEach(function(word) {
    // Keep track of current format
    var format = word.match(/^\[\[([^\]]+)\]/g),
      wordWithFormatting, wordLength;
    if (format !== null && format[0]) {
      currentFormat = format[0];
      word = word.slice(format[0].length);
    }
    // Apply current format to each word separatly
    wordLength = word.length;
    wordWithFormatting = (currentFormat || '') + word;
    if (currentFormat) {
      if (word.indexOf(']') !== -1) {
        wordLength--;
        currentFormat = null;
      } else {
        wordWithFormatting += ']';
      }
    }
    // Assemble line
    if (currentLineLengthWithoutFormatting + wordLength <= length) {
      // Word still fits on current line
      if (currentLineLengthWithoutFormatting > 0) {
        currentLine += ' ';
        currentLineLengthWithoutFormatting++;
      }
    } else {
      // Need to start new line
      result.push(currentLine);
      currentLine = '';
      currentLineLengthWithoutFormatting = 0;
    }

    currentLine += wordWithFormatting;
    currentLineLengthWithoutFormatting += wordLength;
  });

  if (currentLineLengthWithoutFormatting > 0)
    result.push(currentLine);

  return result;
};