Standard library / stdio streams · on the one-page reference

stdio streams

Experimental — new, manually tested rather than conformance-suite covered.

process.stdin()/stdout()/ stderr() reuse the exact ReadableStream/ WritableStream types fs.createReadStream/createWriteStream return, just wired to the process's real stdio file descriptors instead of an opened file — every method below (.read()/ .close()/.write()) already works on them. stdout()/stderr() flush after every .write() call (unlike a file-backed WritableStream, which still buffers until .close()), so writes interleave correctly, in order, with console.log in the same run.

stdin stdout stderr ReadableStream.readLine
process.stdin() Experimental

→ ReadableStream — each call allocates a fresh wrapper around the same real stdin file descriptor (no shared/ cached instance). .read() (64KB chunks) works exactly as it does on any other ReadableStream; see ReadableStream.readLine() below for line-oriented reading.

const input = process.stdin();
const chunk: string = input.read();
console.log(chunk);
process.stdout() Experimental

→ WritableStream — .write(chunk) flushes immediately, every call, so it interleaves correctly with console.log. Closing it (.close()) closes the real stdout fd — usually not something a program needs to do before it exits.

console.log("before");
process.stdout().write("interleaved\n");
console.log("after");
process.stderr() Experimental

→ WritableStream — same shape as process.stdout(), wired to fd 2 instead of fd 1.

process.stderr().write("warning: low disk space\n");
ReadableStream.readLine() Experimental

→ string — available on any ReadableStream (process.stdin() or fs.createReadStream(...) alike). Returns the next line with its trailing \n/\r\n kept, not stripped — deliberate: stripping it would make a genuinely blank line indistinguishable from real end-of-stream (both would be ""), silently truncating a while (line != "") read loop on ordinary blank input lines. "" means true EOF only; call .trim() for a stripped line. A final line with no trailing newline (a piped input cut off mid-line) is still returned intact, not dropped.

const input = process.stdin();
while (true) {
  const raw: string = input.readLine();
  if (raw == "") {
    break;
  }
  console.log(raw.trim());
}