JavaScript | Adding days in milliseconds to Date object

Last Updated : 23 May, 2019

Given a date, the task is to add days in milliseconds to it. To add days in milliseconds to date object in JavaScript, some methods are used which are listed below:

JavaScript getMilliseconds() Method: This method returns the milliseconds (from 0 to 999) of the provided date and time.
Syntax:
```
Date.getMilliseconds()
```
Return value: It returns a number, from 0 to 009, representing the milliseconds.
JavaScript setMilliseconds() Method: This method sets the milliseconds of a date object.
Syntax:
```
Date.setMilliseconds(millisec)
```
Parameters: It accepts single parameter millisec which is required. It specifies the integer value representing the milliseconds. The expected values are 0-999, but other values are allowed.
Note: The parameter accepts values apart from their range and these values works like:
- millisec = -1, it means the last millisecond of the previous second and same for the other parameters.
- If millisec passed as 1000, it means the first millisecond of the next second and same for the other parameters.
Return value: It returns a number, denoting the number of milliseconds between the date object and midnight January 1 1970.
JavaScript getTime() method: This method returns the number of milliseconds between midnight of January 1, 1970, and the specified date.
Syntax:
```
Date.getTime()
```
Return value: It returns a number, representing the number of milliseconds since midnight January 1, 1970.

JavaScript setTime() method: This method sets the date and time by adding/subtracting a defines number of milliseconds to/from midnight January 1, 1970.

Syntax:

Date.setTime(millisec)

Parameters: It accepts single parameter millisec which is required. It specifies the number of milliseconds to be added/subtracted, in midnight January 1, 1970

Return value: It returns the number of milliseconds between the date object and midnight January 1 1970.

Example 1: This example added 1 day in milliseconds to the var today by using setTime() and getTime() method.

<!DOCTYPE HTML> 
<html> 
    <head> 
        <title> 
            JavaScript | Adding days in milliseconds to Date object
        </title>
    </head> 
      
    <body style = "text-align:center;"> 
          
        <h1 style = "color:green;" > 
            GeeksForGeeks 
        </h1>
          
        <p id = "GFG_UP" style = "font-size: 15px; font-weight: bold;">
        </p>
          
        <button onclick = "gfg_Run()"> 
            addMilliseconds
        </button>
          
        <p id = "GFG_DOWN" style = 
            "color:green; font-size: 20px; font-weight: bold;">
        </p>
          
        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
            var today = new Date();
            el_up.innerHTML = "Date = " + today;
              
            Date.prototype.addMillisecs = function(d) { 
                this.setTime(this.getTime() + (d)); 
                return this; 
            }
              
            function gfg_Run() {
                var a = new Date();
                var d = 1;
                a.addMillisecs(d*24*60*60*1000);
                el_down.innerHTML = a;
            }         
        </script> 
    </body> 
</html>                    

Output:

Before clicking on the button:
After clicking on the button:

Example 2: This example added 5 days in milliseconds to the var today by using setMilliseconds() and getMilliseconds() method.

<!DOCTYPE HTML> 
<html> 
    <head> 
        <title> 
            JavaScript | Adding days in milliseconds to Date object
        </title>
    </head> 
      
    <body style = "text-align:center;"> 
      
        <h1 style = "color:green;" > 
            GeeksForGeeks 
        </h1>
          
        <p id = "GFG_UP" style = "font-size: 15px; font-weight: bold;">
        </p>
          
        <button onclick = "gfg_Run()"> 
            addMilliseconds
        </button>
          
        <p id = "GFG_DOWN" style =
            "color:green; font-size: 20px; font-weight: bold;">
        </p>
          
        <script>
            var el_up = document.getElementById("GFG_UP");
            var el_down = document.getElementById("GFG_DOWN");
            var today = new Date();
            el_up.innerHTML = "Date = " + today;
              
            Date.prototype.addMillisecs= function(s) {
                this.setMilliseconds(this.getMilliseconds()+s);
                return this;
            }
              
            function gfg_Run() {
                var a = new Date();
                var d = 5;
                a.addMillisecs(d*24*60*60*1000);
                el_down.innerHTML = a;
            }         
        </script> 
    </body> 
</html>                    

Output:

Before clicking on the button:
After clicking on the button:

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JavaScript | Adding days in milliseconds to Date object

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