Javascript Date Function Not working

Question

Hi I am trying to add 31 days to 'myDate' which is the current date. It is supposed to get the date add 31 days, then the convertDate function is supposed to translate it to something like 'Nov 31, 2012'. But it doesn't work. Does anyone know why?

Here is the primary function...

function process (infoarray) {
  var myDate = new Date();
  //var final = convertDate(myDate);

  var length = infoarray.length;
  var final_string;
  for (var b = 0; b < length; b++) {
    if (b == 0) {
      if (infoarray[b][3] == 'After') {
        final_string = '<b>' + infoarray[b][3] + '&nbsp;' + infoarray[b][1] + '</b><br/>' + infoarray[b][0] + '<br/>';
      } else {
        final_string = '<b>' + infoarray[b][1] + '&nbsp;' + infoarray[b][3] + '&nbsp;' + infoarray[b][2] + '</b><br/>' + infoarray[b][0] + '<br/>';
      }
    } else {
      if (infoarray[b][3] == 'After') {

        final_string = final_string + '<br/><b>' + infoarray[b][3] + '&nbsp;' + convertDate(myDate.setDate(myDate.getDate() + 31)) + '</b><br/>' + infoarray[b][0] + '<br/>';
      } else {
        final_string = final_string + '<br/><b>' + infoarray[b][1] + '&nbsp;' + infoarray[b][3] + '&nbsp;' + infoarray[b][2] + '</b><br/>' + infoarray[b][0] + '<br/>';
      }
    }
  }
  return final_string;
}

Here is the line i am focused on from the function above...

final_string = final_string + '<br/><b>' + infoarray[b][3] + '&nbsp;' + convertDate(myDate.setDate(myDate.getDate() + 31)) + '</b><br/>' + infoarray[b][0] + '<br/>';

Here is the convertDate function...

function convertDate(d) {
    var day = d.getDate();
    if (day < 10) {
        day = '0' + day;
    }
    var year = d.getFullYear();
    var month = d.getMonth();
    var months=['Jan','Feb','Mar','Apr','May','June','July','Aug','Sep','Oct', 'Nov','Dec'];
    var currentMonth = months[month];
    return (currentMonth + ' ' + day + ', ' + year);
}

Why doesn't it work? Any error message in the console? What is the output? — BenM
– BenM, Commented Oct 30, 2012 at 15:08

SLaks · Accepted Answer · 2012-10-30 15:08:58Z

2

myDate.setDate(...) modifies the value of the Date instance, but doesn't return anything.
You need to call setDate first, then pass the variable to your function.

answered Oct 30, 2012 at 15:08

SLaks

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3 Comments

John Doe Over a year ago

I tried this myDate.setDate(convertDate(myDate.getDate() + 31)) but it didn't work either..

John Doe Over a year ago

do you know what the fix would look like?

Onur Topal Over a year ago

convertDate(myDate.setDate(myDate.getDate() + 31)) to myDate.setDate(myDate.getDate() + 31); convertDate(myDate)

mplungjan · Accepted Answer · 2012-10-30 20:47:26Z

1

Here. First calculate then call

DEMO;

var myDate = new Date();
myDate.setDate(myDate.getDate()+31);

final_string = final_string + '<br/><b>' +
infoarray[b][3] + '&nbsp;' + 
convertDate(myDate) + '</b><br/>' + infoarray[b][0] + '<br/>';

Or add it to the function:

.... convertDate(myDate,31) + ....

With

function convertDate(d,offset) {
 if ( offset ) d.setDate(d.getDate()+offset);
 var day = d.getDate();

 if (day < 10) {
    day = '0' + day;
 }
 var year = d.getFullYear();
 var month = d.getMonth();
 var months=['Jan','Feb','Mar','Apr','May','June','July','Aug','Sep','Oct', 'Nov','Dec'];
 var currentMonth = months[month];
 return (currentMonth + ' ' + day + ', ' + year);
}

DEMO

edited Oct 30, 2012 at 20:47

answered Oct 30, 2012 at 15:23

mplungjan

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6 Comments

John Doe Over a year ago

I need to be able to use myDate as the current date over and over again..So I don't want to permanently change it.

John Doe Over a year ago

Therefore in this specific part of the code I pointed out I need to get the current date add any number (ex: 31) to it and return it

John Doe Over a year ago

I tried adding this but it didn't work... convertDate(infoarray[b][1].setDate(myDate.getDate() + 31))

mplungjan Over a year ago

So add it in convert date function convertDate(d,offset) { if ( offset ) d.setDate(d.getDate()+offset); var day = d.getDate();

John Doe Over a year ago

Can you display what the convertDate function would look like?

|

BiAiB · Accepted Answer · 2012-10-30 15:16:49Z

0

By using setDate, you tell the Date object to set the day number to something between 32 and 62, which doesn't make much sense.

A good way to add 31 days would be to use getTime, which returns the number of mseconds ellapsed since 1st Jan 1970:

myDate.setTime( myDate.getTime()+31*24*60*60*1000 );
//31Days x 24 hours x 60 minutes x 60 seconds x 1000 msecs

answered Oct 30, 2012 at 15:16

BiAiB

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4 Comments

John Doe Over a year ago

I see..how would I apply the convertDate function to this too?

mplungjan Over a year ago

No need. Setting a date to 62 will add 31 days to the 31st so will work

BiAiB Over a year ago

well, mdn fooled me (developer.mozilla.org/en-US/docs/JavaScript/Reference/…) . I checked up ecma-international.org/ecma-262/5.1/#sec-15.9.1.12 and you're right. the argument passed to setDate isn't constrained

mplungjan Over a year ago

I do do see where this is fooling you "If the parameter you specify is outside of the expected range, setDate attempts to update the date information in the Date object accordingly. For example, if you use 0 for dayValue, the date will be set to the last day of the previous month."

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