How do I get the difference between two Dates in JavaScript?

Question

I\'m creating an application which lets you define events with a time frame. I want to automatically fill in the end date when the user selects or changes the start date.

Answer 1

JavaScript perfectly supports date difference out of the box

https://jsfiddle.net/b9chris/v5twbe3h/

var msMinute = 60*1000, 
    msDay = 60*60*24*1000,
    a = new Date(2012, 2, 12, 23, 59, 59),
    b = new Date("2013 march 12");


console.log(Math.floor((b - a) / msDay) + ' full days between'); // 364
console.log(Math.floor(((b - a) % msDay) / msMinute) + ' full minutes between'); // 0

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Now some pitfalls. Try this:

console.log(a - 10); // 1331614798990
console.log(a + 10); // mixed string

So if you have risk of adding a number and Date, convert Date to number directly.

console.log(a.getTime() - 10); // 1331614798990
console.log(a.getTime() + 10); // 1331614799010

My fist example demonstrates the power of Date object but it actually appears to be a time bomb