JAVASCRIPT

javascript change input value jquery

$('#IdOfTheField').on('change', function() {
  alert( this.value );
});

assign input text value jquery

   <?= $this->Form->input('number_six', array(
     'label' => false,
     'class' => 'form-control number_six',
     'maxlength' => "1" ,
     'oninput' => "this.value=this.value.replace(/[^0-9]/g,'');"
   ));?>

$(".number_six").val("");