Write buffer to the file.
The promise is fulfilled with an object containing two properties:
It is unsafe to use filehandle.write() multiple times on the same file without waiting for the promise to be fulfilled (or rejected). For this scenario, use filehandle.createWriteStream().
On Linux, positional writes do not work when the file is opened in append mode. The kernel ignores the position argument and always appends the data to the end of the file.