JavaScript setDate function is one of the Date Function, which is used to set the Day number of a given date as per local time. The syntax of the JavaScript setDate function is:
Date.setDate(Day_Number)
JavaScript setDate Function Example
Here, we used the setDate function to set the current day to 25th.
<!DOCTYPE html> <html> <head> <title> JavaScript Set Date Functions </title> </head> <body> <h1> Example </h1> <script> var dt = Date(); document.write("Date and Time : " + dt + "<br/>"); dt.setDate(25); document.write("After : " + dt); </script> </body> </html>
Example
Date and Time: Mon Nov 05 2018 11:45:07 GMT+0530 (Indian Standard Time)
After : Sun Nov 25 2018 11:45:07 GMT+0530 (Indian Standard Time)
JavaScript set Date Example 2
In this JavaScript setDate function example, we set the day number of a custom date to 31
<!DOCTYPE html> <html> <head> <title> JavaScript Set Date Functions </title> </head> <body> <h1> JavaScript setDate Function Example </h1> <script> var dt = Date("December 1, 2016 10:11:22"); document.write("Date and Time : " + dt + "<br/>"); dt.setDate(31); document.write("After setDate() : " + dt); </script> </body> </html>

In this JavaScript set Date example, we set the day number of custom date (without Day or Month) to 31.
<!DOCTYPE html> <html> <head> <title> JavaScript Set Date Functions </title> </head> <body> <h1> Example3 </h1> <script> var dt = Date("2016 10:11:22"); document.write("DateTime : " + dt + "<br/>"); dt.setDate(31); document.write("After : " + dt); </script> </body> </html>
Example3
DateTime: Fri Jan 01 2016 10:11:22 GMT+0530 (Indian Standard Time)
After: Sun Jan 31 2016 10:11:22 GMT+0530 (Indian Standard Time)