How to check if time overlaps in javascript

Question

Hi i am working on Reactjs Application where user needs to select four time slots .Like slot1 starting time, slot2 starting time ,slot1 ending time ,slot2 ending time. I need to check that the slot1 time and slot2 time should not overlap each other. And Starting time of each slot should be greater than of that slot end time

Like if user selects 
slot1  time 10:00 AM- 12:00PM
slot2 time 8:00Am - 9:00 AM.   
it should works in this case



 const chec = () => {
    var a = moment(slot1StartTime).format("hh:mm a");
    var b = moment(slot1EndTime).format("hh:mm a");
    var c = moment(slot2StartTime).format("hh:mm a");
    var d = moment(slot2EndTime).format("hh:mm a");
    var diff = moment
      .duration(moment(a, "hh:mm a").diff(moment(b, "hh:mm a")))
      .asMinutes();
    var diff2 = moment
      .duration(moment(c, "hh:mm a").diff(moment(d, "hh:mm a")))
      .asMinutes();
    var diff3 = moment
      .duration(moment(b, "hh:mm a").diff(moment(c, "hh:mm a")))
      .asMinutes();
   
   
 
    if (diff > 0 || diff2 > 0 || diff3 > 0) {
      
        console.log("error");
      
    }
  };