convert javascript to work on LiveCycle designer

Hi, I'm using the below javascript in adobe form. now I want to use the same code with the LiveCycle designer form but I don't know how to modify this code for LiveCycle. can you pls help me to do it? thanks.

var v1 = Number(this.getField("undefined_2").value);
if (v1==0) event.value = "";
else event.value = 100 - v1;