Document: readyState property

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.

Value

The readyState of a document can be one of following:

loading: The document is still loading (that is, the HTML parser is still working).
interactive: The document has been parsed but sub-resources such as deferred and module scripts, images, stylesheets, and frames are still loading. Once in this state, and the deferred and module scripts have executed, the DOMContentLoaded event fires.
complete: The document and all sub-resources have finished loading. The state indicates that the load event is about to fire.

Examples

undefined

Different states of readiness

switch (document.readyState) {
  case "loading":
    // The document is loading.
    break;
  case "interactive": {
    // The document has finished loading and we can access DOM elements.
    // Sub-resources such as scripts, images, stylesheets and frames are still loading.
    const 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;
}

readystatechange as an alternative to DOMContentLoaded event

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

readystatechange as an alternative to load event

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

readystatechange as event listener to insert or modify the DOM before DOMContentLoaded

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

Specifications

HTML