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.

Value

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 scripts, images, stylesheets and frames are still loading. The state indicates that the DOMContentLoaded event is about to fire.
complete: The document and all sub-resources have finished loading. The state indicates that the load event is about to fire.

Examples

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

Specification
HTML Standard # current-document-readiness

Browser compatibility

BCD tables only load in the browser