text-align-justify.js

const justify = (s, length) => {
  s = s.replace(/\n/g, ' ')
  s = s.split` `;
  const res = [];
  let line = [];
  let words = 0;

  for (let i = 0; i < s.length; i++) {
    if (words + line.length - 1 + s[i].length < length) {
      line.push(s[i]);
      words += s[i].length;
    } else {
      const spaces = [];
      for (let j = 0; j < line.length - 1; j++) spaces.push` `;
      for (let j = 0; j < length - words - line.length + 1; j++)
        spaces[j % (line.length - 1)] += ' ';
      let l = '';
      for (let j = 0; j < line.length; j++) {
        if (j > 0) l += spaces[j - 1];
        l += line[j];
      }
      res.push(l);
      line = [];
      words = 0;
      i -= 1;
    }
  }
  
  if (line.length > 0) res.push(line.join` `);
  
  return res.join`\n`;
};