Question

I’m having a problem with the Date object in JavaScript. I’ve tested it in Firefox and IE.

The following code shows the problem:

alert(new Date(Date.UTC(2011,6,5,1,0,0,0)).getUTCDay().toString());

I’m expecting 0 since 5 June 2011 is Sunday, but it returns 2 thinking it is Tuesday. Do you know why?

Answer 1

Months start at 0, not 1.

So you’re looking at July, not June. 5th July will be a Tuesday.

alert(new Date(Date.UTC(2011,6-1,5,1,0,0,0)).getUTCDay().toString());
// Output: 0

_{(I wrote it out like 6-1 rather than just 5 to make it clear what I’ve changed.)}

The documentation is your friend. Read it whenever you use a function, especially if you run into trouble.