The lastModified
property of the Document
interface returns a string containing the date and time on which the current document was last modified.
The lastModified
property of the Document
interface returns a string containing the date and time on which the current document was last modified.
A string.
This example alerts the value of lastModified
.
js
alert(document.lastModified); // returns: Tuesday, December 16, 2017 11:09:42
This example transforms lastModified
into a Date
object.
js
let oLastModif = new Date(document.lastModified);
This example transforms lastModified
into the number of milliseconds since January 1, 1970, 00:00:00, local time.
js
let nLastModif = Date.parse(document.lastModified);
Note that as a string, lastModified
cannot easily be used for comparing the modification dates of documents. Here is a possible example of how to show an alert message when the page changes (see also: JavaScript cookies API):
js
// Match 'timestamp' in 'last_modif=timestamp' // e.g. '1687964614822' in 'last_modif=1687964614822' const pattern = /last_modif\s*=\s*([^;]*)/; if ( Date.parse(document.lastModified) > (parseFloat(document.cookie.match(pattern)?.[1]) || 0) ) { document.cookie = `last_modif=${Date.now()}; expires=Fri, 31 Dec 9999 23:59:59 GMT; path=${ location.pathname }`; alert("This page has changed!"); }
…the same example, but skipping the first visit:
js
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)) { alert("This page has been changed!"); } }
Note: WebKit returns the time string in UTC; Gecko returns a time in the local timezone. (See: Bug 4363 – document.lastModified returns date in UTC time, but should return it in local time)
If you want to know whether an external page has changed, please read this paragraph about the XMLHttpRequest()
API.
Specification |
---|
HTML Standard # dom-document-lastmodified-dev |
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
lastModified |
1 | 12 | 1 | 4 | ≤12.1 | 1 | 4.4 | 18 | 4 | ≤12.1 | 1 | 1.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/Document/lastModified