code: function foldString(string, width) {
    // In folded style, $k$ consecutive newlines output as $k+1$ newlines—
    // unless they're before or after a more-indented line, or at the very
    // beginning or end, in which case $k$ maps to $k$.
    // Therefore, parse each chunk as newline(s) followed by a content line.
    var lineRe = /(\n+)([^\n]*)/g;
  
    // first line (possibly an empty line)
    var result = (function () {
      var nextLF = string.indexOf('\n');
      nextLF = nextLF !== -1 ? nextLF : string.length;
      lineRe.lastIndex = nextLF;
      return foldLine(string.slice(0, nextLF), width);
    }());
    // If we haven't reached the first content line yet, don't add an extra \n.
    var prevMoreIndented = string[0] === '\n' || string[0] === ' ';
    var moreIndented;
  
    // rest of the lines
    var match;
    while ((match = lineRe.exec(string))) {
      var prefix = match[1], line = match[2];
      moreIndented = (line[0] === ' ');
      result += prefix
        + (!prevMoreIndented && !moreIndented && line !== ''
          ? '\n' : '')
        + foldLine(line, width);
      prevMoreIndented = moreIndented;
    }
  
    return result;
  }
docs: Note: a long line without a suitable break point will exceed the width limit. Pre-conditions: every char in str isPrintable, str.length > 0, width > 0.