Javascript - Custom Format and Keystroke Script

Hello,

I have a field with a custom keystroke:

if( event.willCommit )
{
   if(event.value == "")
     //if nothing is chosen in box1 then box2 will be cleared
     this.getField("Text412").clearItems();
   else
    SetFieldValues(event.value);
}

I would also like this same field to be formatted with two places after the decimal. I am assuming I would need to add code to the Custome format Format script to accomplish that but I don't know how or what scritp to write. Since I don't know how to write javascript I just search and try to adapt what I find. I found this talking about a custome format script:Archived Forum Answer (2 places after decimal)

So I thought I just needed to add this line

Number(event.value).toFixed(2);

to the custom format script but it doesn't work. Is it because I need to add more to the script? Or is my approach completely wrong anyway? Any guidance would be appreciated!

Thanks!

Ariel