JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="splitLines"></textarea>

JavaScript

var textarea = document.getElementById("splitLines");
textarea.onkeyup = function() {
  var lines = textarea.value.split("\n");
  for (var i = 0; i < lines.length; i++) {
    if (lines[i].length <= 16) continue;
    var j = 0; space = 16;
    while (j++ <= 16) {
      if (lines[i].charAt(j) === " ") space = j;
    }
    lines[i + 1] = lines[i].substring(space + 1) + (lines[i + 1] || "");
    lines[i] = lines[i].substring(0, space);
  }
  textarea.value = lines.slice(0, 6).join("\n");
};