The hasFocus()
method of the Document
interface returns a boolean value indicating whether the document or any element inside the document has focus. This method can be used to determine whether the active element in a document has focus.
Note: When viewing a document, an element with focus is always the active element in the document, but an active element does not necessarily have focus. For example, an active element within a popup window that is not the foreground doesn't have focus.
false
if the active element in the document has no focus; true
if the active element in the document has focus.
The following example checks whether the document has focus or not. A function called checkPageFocus()
updates a paragraph element depending on the result of document.hasFocus()
. Opening a new window will cause the document to lose focus and switching back to the original window will cause the document to regain focus.
<p id="log">Focus check results are shown here.</p>
<button id="newWindow">Open new window</button>
const body = document.querySelector("body");
const log = document.getElementById("log");
function checkDocumentFocus() {
if (document.hasFocus()) {
log.textContent = "This document has focus.";
body.style.background = "white";
} else {
log.textContent = "This document does not have focus.";
body.style.background = "gray";
}
}
function openWindow() {
window.open(
"https://developer.mozilla.org/",
"MDN",
"width=640,height=320,left=150,top=150",
);
}
document.getElementById("newWindow").addEventListener("click", openWindow);
setInterval(checkDocumentFocus, 300);