How to get the time span between two date picker values in Javascript?

Question

I've added two Bootstrap Datetime pickers to a HTML5 form. So far I can capture the DateTime value of each picker using the change event of the control.

Now I have a case where the time span difference between both DateTime pickers needs to be stored as a var.

I did come across an example similar to this ask here . But my short implementation below alerts a value of "Nan" instead of the expected time span difference when the actual time picker value is changed.

Question:

How can you calculate the time span between two date picker values in Javascript or JQuery?

Code gist:

var start;
var actual;

$("#OutageStartDisplay").on("dp.change", function (e) {
    start = $('#OutageStart').val(moment(e.date).format());
});


//On change of the ActualDisplay datetime picker 
//update's the Actual hidden field with the datetime.
$("#ActualDisplay").on("dp.change", function (e) {
    actual = $('#Actual').val(moment(e.date).format());

    //If the actual is set, calculate the outage duration
    var timeDiff = Math.abs(start - actual);
    var diffDays = Math.ceil(timeDiff / (1000 * 3600 * 24)); 
    alert(diffDays);

});

Answer 1

Since you're using moment, you can use moment.diff to get the time difference.

Your code also seems a bit bugged, when you do $("whatever").val(something) , you're setting "whatever" s value to something and it returns $("whatever") , not the value. So you're trying to subtract a JQuery object from another JQuery object. But even if it returned the val, your val is a string - which you also cannot substract.

So you probably want this instead:

var start;
var actual;

$("#OutageStartDisplay").on("dp.change", function (e) {
    start = moment(e.date);
    $('#OutageStart').val(start.format());
});

$("#ActualDisplay").on("dp.change", function (e) {
    actual = moment(e.date);
    $('#Actual').val(actual.format());

    //If the actual is set, calculate the outage duration
    alert(actual.diff(start));
});