How to read keystrokes from stdin at Deno

When using Deno, there was a case where I wanted to process input one character at a time.

I don't fully understand the code yet, so the code itself could be improved, but this is how it worked.

Deno.setRaw(0, true);

const bufferSize = 16;
const buf = new Uint8Array(bufferSize);

let output = "";

while (true) {
  const nread = await Deno.stdin.read(buf);

  if (nread === null) {
    console.log("nread is null");
    console.log("Exit");
    break;
  }

  // If you press Ctrl + C, the process will exit.
  if (buf && buf[0] === 0x03) {
    console.log("Ctrl+C");
    console.log("Exit");
    break;
  }

  // If the Enter key is pressed,
  // the text of the output will be displayed and the process will be terminated.
  if (buf && buf[0] === 13) {
    console.log("Ouput: ", output);
    break;
  }

  const text = new TextDecoder().decode(buf.subarray(0, nread));
  output = output + text;
  console.log(output);
}

Deno.setRaw(0, false);

If you want to use Deno.setRaw, you need to run it with the --unstable option.

deno run --unstable sample.ts

Here are some additional explanations for the code above.

• One by one, the entered characters will be added to the variable of output.
• Press Ctrl + C to finish the process.
• Pressing the Enter key will do the same, but the process will end after outputting the string from the variable of output.
• I haven't been able to track when the nread variable returns null, but since there is a possibility that it will return null, I've included the processing for that.
• There is no particular reason for the bufferSize to be 16.