var ar = new Array();
ar[0] = "Sunday";
ar[1] = "Monday";
ar[2] = "Tuesday";
ar[3] = "Wednesday";
ar[4] = "Thursday";
ar[5] = "Friday";
ar[6] = "Saturday";
var birthDay = new Date("January 3, 1978");
var day = birthDay.getDay();
alert("You were born on " + ar[day]);

Notice that Sunday is the first day of the week and its index is 0. Similarly, the first month of the year is January and its numeric value is 0 as well. The following script sets the year, month, and date of the month:

var ar = new Array();
ar[0] = "Sunday";
ar[1] = "Monday";
ar[2] = "Tuesday";
ar[3] = "Wednesday";
ar[4] = "Thursday";
ar[5] = "Friday";
ar[6] = "Saturday";
var birthDay = new Date();
birthDay.setYear(1978);
birthDay.setMonth(0);
birthDay.setDate(3);
var day = birthDay.getDay();
alert("You were born on " + ar[day]);

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