title: increase number when I press arrow key on keyboard with javascript
body: <p>I have a textbox has a numeric value. 
  now what I want is to keep increasing that numeric value while im pressing and holding any of arrow keys. 
  I know how to do this if I was pressing only one time. it will be increased by 1 only. but what If I want to keep increasing the value while i'm holding the arrow keys. how to do that?</p>
  
  <p>thanks</p>