JavaScript を使用して Cookie を設定および取得するにはどうすればよいですか?

function setCookie(name, value, days) {
  var expires = "";
  if (days) {
    var date = new Date();
    date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
    expires = "; expires=" + date.toUTCString();
  }
  document.cookie = name + "=" + (value || "") + expires + "; path=/";
}

function getCookie(name) {
  var nameEQ = name + "=";
  var ca = document.cookie.split(";");
  for (var i = 0; i < ca.length; i++) {
    var c = ca[i];
    while (c.charAt(0) == " ") c = c.substring(1, c.length);
    if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length, c.length);
  }
  return null;
}

<select>

// Set the cookie when the user selects a CSS file
function setCSSLayout() {
  var cssFile = document.getElementById("myList").value;
  setCookie("cssFile", cssFile, 7);
}

// Get the cookie and set the CSS file accordingly
function getCSSLayout() {
  var cssFile = getCookie("cssFile");
  if (cssFile) {
    document.getElementById("css").href = cssFile;
  }
}

// Load the previously selected CSS file
window.onload = function () {
  getCSSLayout();
};