JavaScript Document lastModified Property

What You’ll Learn

Document.lastModified is an instance property that returns a string with the date and local time when the current document was last modified. Learn how to display it, convert it to a Date, compare timestamps, and five examples with try-it labs.

Introduction

Want to show visitors when a page was updated? document.lastModified gives you that information as a readable date/time string in the user’s local time zone.

MDN: the property returns a string containing the date and local time on which the current document was last modified. The value often comes from the server’s Last-Modified information (or a fallback the browser provides).

Related Document tutorials: cookie, documentURI, contentType, Document constructor.

Understanding Document.lastModified

An instance property on Document. Its value is a date/time string for the current document.

• Value — string with last-modified date and local time (MDN).
• Display — show it directly in the UI, or format a Date object.
• Parse — new Date(document.lastModified) or Date.parse(...) (MDN).
• Compare — convert to milliseconds first; do not lexicographically compare strings (MDN).
• External pages — use fetch HEAD and the Last-Modified header (MDN).

📝 Syntax

document.lastModified

Value

A string (MDN). Example shape from MDN: Tuesday, December 16, 2017 11:09:42 — exact formatting can vary by browser/locale.

MDN: convert to Date

let oLastModif = new Date(document.lastModified);
let nLastModif = Date.parse(document.lastModified);

⚖️ Related Timing & Meta APIs

Examples Gallery

Examples follow MDN Document: lastModified. Output times vary by when the file was served or saved.

console.log(document.lastModified);
// e.g. Tuesday, December 16, 2017 11:09:42

07/28/2026 18:45:00

let oLastModif = new Date(document.lastModified);

console.log(oLastModif.toString());
console.log(oLastModif.getFullYear());

Tue Jul 28 2026 ...
2026

let nLastModif = Date.parse(document.lastModified);

console.log(nLastModif);
console.log(Number.isNaN(nLastModif) ? "unparsable" : "ok");

1753702500000
ok

const updated = new Date(document.lastModified);

console.log(
  "Updated: " + updated.toLocaleString(undefined, {
    dateStyle: "medium",
    timeStyle: "short"
  })
);

Updated: Jul 28, 2026, 6:45 PM

const pattern = /last_modif\s*=\s*([^;]*)/;
const lastVisit = parseFloat(document.cookie.replace(pattern, "$1"));
const lastModif = Date.parse(document.lastModified);

if (Number.isNaN(lastVisit) || lastModif > lastVisit) {
  document.cookie =
    "last_modif=" + Date.now() +
    "; expires=Fri, 31 Dec 9999 23:59:59 GMT; path=" + location.pathname;

  if (isFinite(lastVisit)) {
    console.log("This page has been changed!");
  } else {
    console.log("First visit — timestamp saved.");
  }
} else {
  console.log("No change since last visit.");
}

First visit — timestamp saved.

🚀 Common Use Cases

• Footer “Updated” line — show when the article was last modified.
• Changelog hints — prompt returning visitors that content changed.
• Cache debugging — confirm whether a refreshed page looks newer.
• Static sites — surface file modification time from the server.
• External monitoring — HEAD + Last-Modified for other URLs (MDN).
• Admin tools — list page freshness during content reviews.

📝 Notes

• MDN: Baseline Widely available (since July 2015) — no Deprecated / Experimental / Non-standard banner.
• Do not compare raw strings for sorting — parse first (MDN).
• String format can vary by browser; treat it as opaque until parsed.
• For other URLs, use fetch HEAD and inspect Last-Modified (MDN).
• Related: cookie, lastElementChild, documentURI, Document constructor.

💡 Best Practices