Document.readyState

The Document.readyState property describes the loading state of the document.

When the value of this property changes, a readystatechange event fires on the document object.

var string = document.readyState;

The readyState of a document can be one of following:

loading

The document is still loading.

interactive

The document has finished loading and the document has been parsed but sub-resources such as images, stylesheets and frames are still loading.

complete

The document and all sub-resources have finished loading. The state indicates that the load event is about to fire.

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.
    // But sub-resources such as images, stylesheets and frames are still loading.
    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();
  }
}

document.addEventListener('readystatechange', event => {
  if (event.target.readyState === 'interactive') {
    initLoader();
  }
  else if (event.target.readyState === 'complete') {
    initApp();
  }
});

• readystatechange event
• DOMContentLoaded event
• load event