JavaScript | Adding days in milliseconds to Date object

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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