javascript - toISOString() return wrong date

Question

Why did this piece of code return tomorrow's date ?

It must return 2013-08-31 and not 2013-09-01 as we are August 31st.

http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_toisostring

function myFunction() {
  var d = new Date();
  var x = document.getElementById("demo");
  x.innerHTML = d.toISOString();
}

<p id="demo">Click the button to display the date and time as a string, using the ISO
  standard.</p>
<button onclick="myFunction()">Try it</button>

Answer 1

It's in UTC.

If you want to get your local timezone you have to format the date yourself (using getYear() getMonth() etc.) or use some library like date.js that will format the date for you.

With date.js it's pretty simple:

(new Date()).format('yyyy-MM-dd')

edit

As @MattJohnson noted date.js has been abandoned, but you can use alternatives like moment.js.