Using File in Typescript

Question

I am writing a web application using Angular 4 and Typescript. I need the date of a file to upload and try to use the File objects lastModified property, but Typescript gives me an error

Property 'lastModified' does not exist on type 'File'.

If I look in the definition it instead have the lastModifiedDate as a property. According to https://developer.mozilla.org/en-US/docs/Web/API/File/lastModifiedDate that property is depriciated. I have however tried it and it works in Chrome, but fails in Safari.

How can I use File lastModified property from Typescript?

Please provide peace of code for people to see if you are doing it right. — komron, Nov 01 '17 at 20:04
But File.lastModified does not exist in lib.dom.d.ts: interface: File extends Blob { readonly lastModifiedDate: any; readonly name: string; readonly webkitRelativePath: string; } — Jørgen Rasmussen, Nov 01 '17 at 20:08

score 5 · Accepted Answer · answered Nov 01 '17 at 20:10

5

Try

interface MyFile extends File {
    lastModified: any;
}

let myFile = <MyFile>originalFile;
let lm = myFile.lastModified;

answered Nov 01 '17 at 20:10

Andrey

559
3
6

cachius · Answer 2 · 2023-06-30T05:07:05.720

Also for lastModifiedDate, which is deprecated but for now still around in Chrome and was the only option in IE:

// use non-deprecated lastModified field instead 
new Date(file.lastModified)


// in-line type assertion
(file as unknown as { lastModifiedDate: Date }).lastModifiedDate

// type assertion with special type
type DateFile = File & {
  lastModifiedDate: Date;
};
...
(file as DateFile).lastModifiedDate

will prevent TS2551 Property 'lastModifiedDate' does not exist on type 'File'. Did you mean 'lastModified'? ts(2551) error by using lastModified instead or asserting that it exists.

Using File in Typescript

2 Answers2