Node.js stdin — Manual vs Automatic Data Reading

Stream Modes

Paused Mode (default)

• No “data” events
• Node waits for you to request data
• You must pull data manually using .read()
• Triggered by default unless you call .resume()

Flowing Mode

• “data” events fire automatically
• Data flows into your program without asking
• Enabled using process.stdin.resume()

Manually Asking for Data (Paused Mode)

Use the “readable” event with .read():

process.stdin.setEncoding("utf8");

process.stdin.on("readable", () => {
  let chunk;
  while ((chunk = process.stdin.read()) !== null) {
    console.log("Got:", chunk);
  }
});

Key points:

• “readable” fires when data is available
• .read() pulls data out of the buffer
• If .read() returns null, no more data is ready
• You control exactly when to read input

Automatically Receiving Data (Flowing Mode)

process.stdin.setEncoding("utf8");
process.stdin.resume();

process.stdin.on("data", (chunk) => {
  console.log("Got:", chunk);
});

Key points:

• Stream pushes data to you
• You don’t call .read()
• Best mode for games, keypress handling, and interactive apps