If/then statement when clicking submit button

Hello,

I'm at a loss here and I was wondering if anyone can help. Thank you so much in advance.

I'm looking to check if fieldA which is a dropdown yes or no field. If fieldA is Yes, then do nothing. If fieldA is No, then get the date and time and convert it to a hexidecimal value. What is wrong with my script?

var fieldA = this.getField("Resubmission").value;
var hexString = this.getField("LRFNO").value;
if (fieldA = "Yes") {
hexString = "";
}
else {var ts = Math.round((new Date()).getTime() / 1000);
hexString = ts.toString(16).toUpperCase();
}