What is the best way to determine if a date is today in JavaScript?

You could use toDateString:

var d = new Date()
var bool = (d.toDateString() === otherDate.toDateString());

The answers based on toDateString() will work I think, but I personally would avoid them since they basically ask the wrong question.

Here is a simple implementation:

function areSameDate(d1, d2) {
    return d1.getFullYear() == d2.getFullYear()
        && d1.getMonth() == d2.getMonth()
        && d1.getDate() == d2.getDate();
}

MDN has a decent overview of the JS Date object API if this isn't quite what you need.