UNSTABLE: New API, yet to be vetted. This API is under consideration to determine if permissions are required to call it.

Retrieve the process umask. If mask is provided, sets the process umask. This call always returns what the umask was before the call.

console.log(Deno.umask());  // e.g. 18 (0o022)
const prevUmaskValue = Deno.umask(0o077);  // e.g. 18 (0o022)
console.log(Deno.umask());  // e.g. 63 (0o077)

NOTE: This API is not implemented on Windows