Javascript code for showing yesterday's date and todays date

How to show yesterday's date in my textbox the yesterday's date and at the same time, the today's date in ?

I have this home.php where I show the date yesterday(user cannot modify this-readonly) and the date today(user MUST input the date today). And when tomorrow comes and the user visits the home .php s/he will saw the date inputted yesterday, and will input the date again for romorrow's.

E.G: Day1 (march 30, 2011) Yesterday's date: March 29, 2011. (Not editable textbox) Enter date today: (I'll type..) March 30, 2011.

Day 2 (march 31, 2011) Yesterday's date: March 30, 2011. (Not editable textbox) Automatically, this will appear upon hitting the home.php Enter date today: (I'll type..) March 31, 2011.

and so on..

I need a validation that wont accept wrong date format and the format must be: 01-Mar-11 How to do this? :(

Yesterday's date is simply today's date less one, so:

var d = new Date();
d.setDate(d.getDate() - 1);

If today is 1 April, then it is set to 0 April which is converted to 31 March.

Since you also wanted to do some other stuff, here are some functions to do it:

// Check if d is a valid date
// Must be format year-month name-date
// e.g. 2011-MAR-12 or 2011-March-6
// Capitalisation is not important
function validDate(d) {
  var bits = d.split('-');
  var t = stringToDate(d);
  return t.getFullYear() == bits[0] && 
         t.getDate() == bits[2];
}

// Convert string in format above to a date object
function stringToDate(s) {
  var bits = s.split('-');
  var monthNum = monthNameToNumber(bits[1]);
  return new Date(bits[0], monthNum, bits[2]);
}

// Convert month names like mar or march to 
// number, capitalisation not important
// Month number is calendar month - 1.
var monthNameToNumber = (function() {
  var monthNames = (
     'jan feb mar apr may jun jul aug sep oct nov dec ' +
     'january february march april may june july august ' +
     'september october november december'
     ).split(' ');

  return function(month) {
    var i = monthNames.length;
    month = month.toLowerCase(); 

    while (i--) {
      if (monthNames[i] == month) {
        return i % 12;
      }
    }
  }
}());

// Given a date in above format, return
// previous day as a date object
function getYesterday(d) {
  d = stringToDate(d);
  d.setDate(d.getDate() - 1)
  return d;
}

// Given a date object, format
// per format above
var formatDate = (function() {
  var months = 'jan feb mar apr may jun jul aug sep oct nov dec'.split(' ');
  function addZ(n) {
    return n<10? '0'+n : ''+n;
  }
  return function(d) {
    return d.getFullYear() + '-' + 
           months[d.getMonth()] + '-' + 
           addZ(d.getDate());
  }
}());

function doStuff(d) {

  // Is it format year-month-date?
  if (!validDate(d)) {
    alert(d + ' is not a valid date');
    return;
  } else {
    alert(d + ' is a valid date');
  }
  alert(
    'Date in was: ' + d +
    '\nDay before: ' + formatDate(getYesterday(d))
  );
}


doStuff('2011-feb-08');
// Shows 2011-feb-08 is a valid date
//       Date in was: 2011-feb-08
//       Day before: 2011-feb-07

One liner:

var yesterday = new Date(Date.now() - 864e5); // 864e5 == 86400000 == 24*60*60*1000