How to set input type date's default value to today?

Like any HTML input field, the browser will leave the date element empty unless a default value is specified within the value attribute. Unfortunately, HTML5 doesn't provide a way of specifying 'today' in the HTMLInputElement.prototype.value.

One must instead explicitly provide a RFC3339 formatted date (YYYY-MM-DD). For example:

element.value = "2011-09-29"

The JavaScript Date object provides enough built-in support for the required format to avoid doing it manually:

Add this for correct timezone support:

Date.prototype.toDateInputValue = (function() {
    var local = new Date(this);
    local.setMinutes(this.getMinutes() - this.getTimezoneOffset());
    return local.toJSON().slice(0,10);
});

jQuery:

$(document).ready( function() {
    $('#datePicker').val(new Date().toDateInputValue());
});​

Pure JS:

document.getElementById('datePicker').value = new Date().toDateInputValue();