var startDate = document.getElementById("start").value;

var endDate = document.getElementById("end").value;

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var date1 = new Date(startDate);

var date2 = new Date(endDate);

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var diff = date2.getTime() - date1.getTime();

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var days = Math.floor(diff / (1000 * 60 * 60 * 24));

diff -=  days * (1000 * 60 * 60 * 24);

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var hours = Math.floor(diff / (1000 * 60 * 60));

diff -= hours * (1000 * 60 * 60);

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var mins = Math.floor(diff / (1000 * 60));

diff -= mins * (1000 * 60);

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var seconds = Math.floor(diff / (1000));

diff -= seconds * (1000);

​

​

console.log(days + " days : " + hours + " hours : " + mins + " minutes : " + seconds + " seconds");

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​