Trigger only on word characters, backspace or delete and an entry size of at least 3 characters

keyup.php

// Search
$('#categoryFilter').on('keyup', function(event) {
  var searchText = $(this).val();
  var c = String.fromCharCode(event.keyCode);
  var isWordCharacter = c.match(/\w/);
  var isBackspaceOrDelete = (event.keyCode == 8 || event.keyCode == 46);
  // Trigger only on word characters, backspace or delete and an entry size of at least 3 characters
  if((isWordCharacter || isBackspaceOrDelete) && searchText.length > 2) {
    console.debug('Searching for ' + searchText);
  }
});