The File.lastModified
read-only property provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.
The File.lastModified
read-only property provides the last modified date of the file as the number of milliseconds since the Unix epoch (January 1, 1970 at midnight). Files without a known last modified date return the current date.
A number that represents the number of milliseconds since the Unix epoch.
The example below will loop through the files you choose, and print whether each file was modified within the past year.
html
<input type="file" id="filepicker" name="fileList" multiple /> <output id="output"></output>
js
const output = document.getElementById("output"); const filepicker = document.getElementById("filepicker"); filepicker.addEventListener("change", (event) => { const files = event.target.files; const now = new Date(); output.textContent = ""; for (const file of files) { const date = new Date(file.lastModified); // true if the file hasn't been modified for more than 1 year const stale = now.getTime() - file.lastModified > 31_536_000_000; output.textContent += `${file.name} is ${ stale ? "stale" : "fresh" } (${date}).\n`; } });
If a File is created dynamically, the last modified time can be supplied in the new File()
constructor function. If it is missing, lastModified
inherits the current time from Date.now()
at the moment the File
object gets created.
js
const fileWithDate = new File([], "file.bin", { lastModified: new Date(2017, 1, 1), }); console.log(fileWithDate.lastModified); // returns 1485903600000 const fileWithoutDate = new File([], "file.bin"); console.log(fileWithoutDate.lastModified); // returns current time
To offer protection against timing attacks and fingerprinting, the precision of someFile.lastModified
might get rounded depending on browser settings. In Firefox, the privacy.reduceTimerPrecision
preference is enabled by default and defaults to 20us in Firefox 59; in 60 it will be 2ms.
js
// reduced time precision (2ms) in Firefox 60 someFile.lastModified; // 1519211809934 // 1519211810362 // 1519211811670 // … // reduced time precision with `privacy.resistFingerprinting` enabled someFile.lastModified; // 1519129853500 // 1519129858900 // 1519129864400 // …
In Firefox, if you enable privacy.resistFingerprinting
, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds
, whichever is larger.
Specification |
---|
File API # dfn-lastModified |
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
lastModified |
13 | 18 | 15 | No | ≤15 | 10 | ≤37 | 18 | 15 | ≤14 | 10 | 1.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/File/lastModified