Browsers provide us a File object.
The File object is a Blob object, and it provides 3 properties on top of it:
name(a String)lastModified(the UNIX timestamp of the last modified date time)
which adds up to the Blob object properties:
size(the size in bytes)type(the MIME type)
You will receive a File object when interacting with the FileList object, which can be retrieved from an HTML Form with an <input type="file" /> element, or when interacting with Drag and Drop.
When you got a FileList object, when you loop over it or you pick an element (for example the first item with myFileList[0]) you will get a File object.
Say you have an input type="file" element in your form:
<input type="file" />
Now you can listen for the change event on this element, so when you choose a file you’ll get information about it. document.querySelector('input').files will return a FileList object, like explained above, and using [0] we get the first file loaded, and we can access all the properties we need from the File object:
document.querySelector('input').addEventListener('change', () => {
const file = document.querySelector('input').files[0]
alert(`The file ${file.name} was last modified on ${new Date(file.lastModified).toDateString()}`)
})
See the Pen File object demo by Flavio Copes (@flaviocopes) on CodePen.
Download my free JavaScript book!
