Question

I know I can detect a single backspace keypress like this:

$("#myelement").bind ("keyup", function(event) {
    if (event.keyCode==8) {
        alert ("Backspaced!!!");
    }
});

How would I detect double backspace that happens say within 1 second, just like double click?

Answer 1

On jQuery.com itself, within their custom.js file, is a bit of code that might be helpful for you. It listens for the “konami” code in the users keystrokes. If it detects a certain sequence of keys, shown below in the variable konami, it responds.

// Hehe.
if (window.addEventListener) {
  var kkeys = [], konami = "38,38,40,40,37,39,37,39,66,65";
  window.addEventListener("keydown", function(e) {
    kkeys.push(e.keyCode);
    if (kkeys.toString().indexOf(konami) >= 0) 
      window.location = "http://ejohn.org/apps/hero/";
  }, true);
}

What this code doesn’t do is track the time between the last keypress, and our current keypress. But note, with a few slight modifications, we can mimic their code and produce the desired output that you want as well.

<script>
  (function($){
    // Prep our variables
    var keys = [], lastEntry = 0, seq = '8,8';
    // Listen for keydown events
    $(document).keydown(function(e){
      // Push new key into keys array
      keys.push(e.which);
      // See if we need to respond
      if ( keys.toString().indexOf(seq) != -1 )
        if ( e.timeStamp - lastEntry <= 1000 )
          console.log( 'Correct keys, in the current time.' );
      // Update time of last keydown
      lastEntry = e.timeStamp;
    });
  })(jQuery);
</script>