Create a border around a text field based on a dropdown selection

Hi,

I have a dropdown with 5 values (1,2,3,4,5). I want the text field next to the dropdown to have a red border if 1 or 2 is selected. I've tried a ton of different scripts.

event.value=this.getField("Text 19").value;

if (event.value=="1")

event.target.borderColor = color.red;

Thank you.