Document.readyState

var string = document.readyState;

switch (document.readyState) {
  case "loading":
    // The document is still loading.
    break;
  case "interactive":
    // The document has finished loading. We can now access the DOM elements.
    var span = document.createElement("span");
    span.textContent = "A <span> element.";
    document.body.appendChild(span);
    break;
  case "complete":
    // The page is fully loaded.
    console.log(
      "The first CSS rule is: " + document.styleSheets[0].cssRules[0].cssText,
    );
    break;
}

// alternative to DOMContentLoaded event
document.onreadystatechange = function () {
  if (document.readyState == "interactive") {
    initApplication();
  }
};

// alternative to load event
document.onreadystatechange = function () {
  if (document.readyState == "complete") {
    initApplication();
  }
};