how to use getDay in a function in javascript code example

Example 1: get day js

switch (new Date().getDay()) {
  case 0:
    day = "Sunday";
    break;
  case 1:
    day = "Monday";
    break;
  case 2:
    day = "Tuesday";
    break;
  case 3:
    day = "Wednesday";
    break;
  case 4:
    day = "Thursday";
    break;
  case 5:
    day = "Friday";
    break;
  case 6:
    day = "Saturday";
}

Example 2: new date getday js

Date.getDay()
// Javascript date getDay() method returns the day of the week for the specified
// date according to local time. The value returned by getDay() is an integer 
// corresponding to the day of the week: 0 for Sunday, 1 for Monday, 2 for Tuesday, and so on.