nodejs how to read keystrokes from stdin


Question

Is it possible to listen for incoming keystrokes in a running nodejs script? If I use process.openStdin() and listen to its 'data' event then the input is buffered until the next newline, like so:

// stdin_test.js
var stdin = process.openStdin();
stdin.on('data', function(chunk) { console.log("Got chunk: " + chunk); });

Running this, I get:

$ node stdin_test.js
                <-- type '1'
                <-- type '2'
                <-- hit enter
Got chunk: 12

What I'd like is to see:

$ node stdin_test.js
                <-- type '1' (without hitting enter yet)
 Got chunk: 1

I'm looking for a nodejs equivalent to, e.g., getc in ruby

Is this possible?

1
105
2/15/2011 5:00:42 PM

Accepted Answer

You can achieve it this way, if you switch to raw mode:

var stdin = process.openStdin(); 
require('tty').setRawMode(true);    

stdin.on('keypress', function (chunk, key) {
  process.stdout.write('Get Chunk: ' + chunk + '\n');
  if (key && key.ctrl && key.name == 'c') process.exit();
});
57
3/13/2012 4:51:46 PM

For those finding this answer since this capability was stripped from tty, here's how to get a raw character stream from stdin:

var stdin = process.stdin;

// without this, we would only get streams once enter is pressed
stdin.setRawMode( true );

// resume stdin in the parent process (node app won't quit all by itself
// unless an error or process.exit() happens)
stdin.resume();

// i don't want binary, do you?
stdin.setEncoding( 'utf8' );

// on any data into stdin
stdin.on( 'data', function( key ){
  // ctrl-c ( end of text )
  if ( key === '\u0003' ) {
    process.exit();
  }
  // write the key to stdout all normal like
  process.stdout.write( key );
});

pretty simple - basically just like process.stdin's documentation but using setRawMode( true ) to get a raw stream, which is harder to identify in the documentation.


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