前提:input 框限制小數點位數是2
var a = ($("#amount").numberbox('getValue') ==null ||$("#amount").numberbox('getValue') == "")?"0.00":$("#amount").numberbox('getValue') ;
var b = ($("#price").numberbox('getValue') ==null ||$("#price").numberbox('getValue') == "")?"0.00":$("#price").numberbox('getValue') ;
var subValue = Number(a - b).toFixed(2);