Deno.resources

Returns a map of open resource ids (rid) along with their string representations. This is an internal API and as such resource representation has any type; that means it can change any time.

console.log(Deno.resources());
// { 0: "stdin", 1: "stdout", 2: "stderr" }
Deno.openSync('../test.file');
console.log(Deno.resources());
// { 0: "stdin", 1: "stdout", 2: "stderr", 3: "fsFile" }