Field Won't Refresh Unless Lose Focus

Hi All,
I want to have a text field show one of a set of 3 values (blank, 2, 4) based on its current value. The values are to cycle in response to successive mouse down events (clicks). The following code seems to work but doesn't refresh the text box value ...
============================================
 
var et = event.target;
 
try{
if (et.value!= undefined)
{
if (et.value == "")
et.value = '2';
else
if (et.value == '2')
event.target.value = '4';
else
event.target.value = '';
}
} catch(err){
app.alert(err.toString());
}
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Thanks for your help.