In Javascript, the `Date` class is used in a variety of ways.

This shot explains how to calculate the number of days between two given dates. This can be achieved in a number of ways, but we will focus on two specific approaches.

#   
## First approach
First, get the internal millisecond value of both dates using the built-in JavaScript `getTime()` function of the `Date` class. Convert both dates to milliseconds using the `getTime()` method of the `Date` class. 

Then, get the difference between both dates and divide the result by one day in a milliseconds value and there you have it. 

Let's see some code snippets.
## Code

// JavaScript program to illustrate 
 // calculation of no. of days between two date 
 
 // To set two dates to two variables
 var date1 = new Date("06/30/2019");
var date2 = new Date("07/30/2019");
 
// To calculate the time difference of two dates
var Difference_In_Time = date2.getTime() - date1.getTime();
 
// To calculate the no. of days between two dates
var Difference_In_Days = Difference_In_Time / (1000 * 3600 * 24);
 
//To display the final no. of days (result)
document.write("Total number of days between dates "
 + date1 + " and " 
 + date2 + " is: " 
 + Difference_In_Days);

codemirror

## Second approach 
 

We can make the calculation outlined in the first approach by creating the present date as an object using the new `Date` class. This new class, with the use of the `get_date()` method, provides us with the present date. 

Then, we will get another date, for example, Christmas day, by using the `Date.getFullYear()` method.


We will set an `if` condition that checks whether we have passed the reference future date, which in this example is Christmas day. If it is already passed, then use the one for next year.

Using the following expression, the result is calculated in milliseconds and then converted into days.

```
Math.round(christmas() – present_date.getTime())/A_day_in_miliseconds
```

In this example we calculated the number of days from now until Christmas day. 
 ### Code


// One day Time in ms (milliseconds)
 var one_day = 1000 * 60 * 60 * 24
 
 // To set present_dates to two variables
 var present_date = new Date();
 
 // 0-11 is Month in JavaScript
 var christmas_day = new Date(present_date.getFullYear(), 11, 25)
 
 // To Calculate next year's Christmas if passed already.
 if (present_date.getMonth() == 11 && present_date.getdate() > 25)
 christmas_day.setFullYear(christmas_day.getFullYear() + 1)
 
 // To Calculate the result in milliseconds and then converting into days
 var Result = Math.round(christmas_day.getTime() - present_date.getTime()) / (one_day);
 
 // To remove the decimals from the (Result) resulting days value
 var Final_Result = Result.toFixed(0);
 
 //To display the final_result value
 document.write("Number of days remaining till christmas " 
 + present_date + " and " 
 + christmas_day + " is: " 
 + Final_Result);

How to calculate the difference in days between two dates in JS

Use JavaScript's `getTime()` method to calculate differences between dates; convert results from milliseconds to days.