Javascript problem

Hi there. I’m a bit disappointed it’s necessary to learn javascript in order to run calculations in this plugin. I’m having trouble with my code (because I don’t know java!)… perhaps someone can tell me why the second line of this code won’t work: (when fieldname4 = 2)

(function(){

if(fieldname4 == 1) return fieldname9*209;
if(fieldname4 == 2) return (0.76+fieldname9)*209;
if (fieldname4 == 3) return fieldname9*40;
if (fieldname4 == 4) return fieldname9*50;

})();

Any pointers appreciated!

https://wordpress.org/plugins/calculated-fields-form/