function download(file){

    return new Promise(resolve => {
        console.log(`started downloading ${file.name}`)

        setTimeout(() => {
            console.log(`downloaded ${file.name} in ${file.downloadTime}ms`);
            resolve();
        },file.downloadTime);
    })

}

const file = new File('example',2000)
download(file).then(_ => console.log('complete'))

// ----- output in console -----
// started downloading example ...(immediately)
// downloaded example in 2000ms ...(after 2s)
// complete ...(after 2s)