What makes it suddenly turn to text?

Question

So below you see the exercise has been completed but I don't get the exact proces behind it. Why does putting the d.getDay in those arrays at the bottom suddenly make it turn into the right text?

function main() {
var year = parseInt(readLine(), 10);
var month = parseInt(readLine(), 10);
var day = parseInt(readLine(), 10);

console.log(getWeekDay(year, month, day));
}

function getWeekDay(year, month, day) {
var names = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
var d = new Date(year, month, day);
return names[d.getDay()];
}

Answer 1

var d = new Date(year, month, day);
creates a date object with the current date.
using d you can access the methods of Date(). to do so you use the object.method() form. d in this case is the object.
d.getDay() returns the current day as an int from 0 to 6. Sunday = 0, Monday = 1,..., Saturday =6.
names[d.getDay()] is equivalent to names[0]. as i'm writing this on Sunday. on Monday it will be equivalent to names[1]. and so on.