Is it possible to upload a file in memory using javascript for processing before sending it to server?

Question

Let's say I want to use some js encryption library (not java) to encrypt a file. Is it possible to do so on client side before sending the file to the server and so upload a file by javascript in some memory on client side ?

Could I use local storage for example at least for latest browsers ?

Answer 1

You could use the File API

Here some examples: https://developer.mozilla.org/en/Using_files_from_web_applications)

Of course, as you imagined, you need latest browsers.

Answer 2

Yes you can. You have a few options to do that though.

Using FormData

const formData = new FormData()
formData.append('file', new Blob([fileTextContent], {type: 'text/plain'}))
await axios.post('/upload-file', formData)

Documentation: https://developer.mozilla.org/en-US/docs/Web/API/FormData/Using_FormData_Objects#creating_a_formdata_object_from_scratch

Set a file <input>'s value

let file = new File([data], "img.jpg",{type:"image/jpeg", lastModified:new Date().getTime()});
let container = new DataTransfer();
container.items.add(file);
fileInputElement.files = container.files;

Then you can submit the form containing the <input> normally.

The code above is from this SO answer: https://stackoverflow.com/a/66466855/14366961