如何检查是否使用JQuery / Javascript设置了datepicker和timepicker元素

I have 2 date picker and 2 respective time pickers in HTML page. So basically, whenever user clicks and selects any single datepicker(and/or timepicker)a function will be caled and it will check if all the 4 respective fields have values within them. I have 2 date picker and 2 respective time pick