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Yuki Shindo
Yuki Shindo

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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;

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

  // If you press Ctrl + C, the process will exit.
  if (buf && buf[0] === 0x03) {

  // 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);

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

Deno.setRaw(0, false);
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If you want to use Deno.setRaw, you need to run it with the --unstable option.

deno run --unstable sample.ts
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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.

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