Detecting an "invalid date" Date instance in JavaScript

I'd like to tell the difference between valid and invalid date objects in JS, but couldn't figure out how: var d = new Date("foo"); console.log(d.toString()); // shows 'Invalid Date' console.log(typeof d); // shows 'object' console.log(d instanceof Date); // shows 'true' Any ideas for writing an isValidDate function? Ash recommended Date.parse for parsing date strings, which gives an authoritative