[JS] exercise at fCC: https://codepen.io/adrianskar/pen/ELLvbP

truncate_a_string.js

function truncateString(str, num) {
  if (num <= 3) {
    return str.substr(0, num) + '...';
  }
  if (num >= str.length) {
    return str;
  }
  return str.substr(0, num - 3) + '...';
}

truncateString('A-tisket a-tasket A green and yellow basket', 11);