Check if date is in the past without submitting form

Question

I have this code that I want to check if a date is in the past. I want to check it as soon as the date is entered, before form submission.

Answer 1

For those who use type="date" (introduced with HTML5) instead of type="text", it can be done this way:

 function checkDate() {
   var date = this.value;
   if(date.valueAsDate <= new Date()) {
       //Date in the past
   } else {
       //Date in the future
   }
}