seek = function() {
        if (offset >= file.size) {
            self.postMessage({"fileBuffer": data.buffer, "inputNum": inputNum, "id": self.id}, [data.buffer]);
            return;
        }
        self.postMessage({"progress": Math.round(offset / file.size * 100), "inputNum": inputNum});
        const slice = file.slice(offset, offset + CHUNK_SIZE);
        reader.readAsArrayBuffer(slice);
    }
Loads a file object into an ArrayBuffer, then transfers it back to the parent thread.

@param {File} file
@param {string} inputNum