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 API The definition of 'lastModified' in that specification. |
Working Draft | Initial definition. |
Browser compatibility
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