Java to javascript file upload

upload.js

export function readFile() {
    let path = Android.imagePath();
    let base64 = Android.imageData();

    // If there is an escaped / in the name, this will produce wrong result
    // but still give proper type
    let filename = path.split('/').pop();
    let type = getType(filename);

    let byteString = atob(base64);
    let intArray = new Uint8Array(byteString.length);
    for (let i = 0; i < byteString.length; i += 1) {
        intArray[i] = byteString.charCodeAt(i);
    }

    let f = {
        _buffer: intArray.buffer,
        size: byteString.length,
        name: filename,
        type
    };

    // Here you can use f the way you want.
    // xhr.send(f._buffer) will work
}

// This is very limited, but enough for my use.
// You might want to add another Java interface to use Android native
// type detection (if such thing exists)
function getType(path: string) {
    if (path.match(/\.png$/)) {
        return "image/png";
    } else if (path.match(/\.jpg$/)) {
        return "image/jpeg";
    } else if (path.match(/\.pdf$/)) {
        return "application/pdf";
    } else {
        return "application/octet-stream";
    }
}