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.
Syntax
const time = instanceOfFile.lastModified;
Value
A number that represents the number of milliseconds since the Unix epoch.
Example
Reading from file input
<input type="file" multiple id="fileInput">
const fileInput = document.querySelector('#fileInput'); fileInput.addEventListener('change', (event) => { // files is a FileList object (similar to NodeList) const files = event.target.files; for (let file of files) { const date = new Date(file.lastModified); console.log(`${file.name} has a last modified date of ${date}`); } });
Try the results out below:
Dynamically created files
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.
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
Reduced time precision
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.
// 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, you can also enabled privacy.resistFingerprinting
, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds
, whichever is larger.
Specifications
Specification | Status | Comment |
---|---|---|
File APIThe definition of 'lastModified' in that specification. | Working Draft | Initial definition. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
lastModified
|
Chrome
Full support 13 |
Edge
Full support 18 |
Firefox
Full support 15 |
IE
No support No |
Opera
Full support 16 |
Safari
Full support 10 |
WebView Android
Full support Yes |
Chrome Android
Full support Yes |
Firefox Android
No support No |
Opera Android
No support No |
Safari iOS
Full support 10 |
Samsung Internet Android
Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
See also
File.lastModified by Mozilla Contributors is licensed under CC-BY-SA 2.5.