JDev

Let’s say you have two text-boxes that show dates, and you need to get a difference between the two. There  is no built-in JavaScript function to calculate the difference but you can easily accomplish it using a few JavaScript functions.

Let’s assume that a date is represented in the following format: mm/dd/yyyy.

First we need to convert this string into a JavaScript Date object. Here is a function that does that.

function convertToDate(str){

    return new Date(year, month, day, 0,0,0);
}

Pass a string to the function and get a Date object back. You may need to modify it depending on your date format and separator used. 

 Now we can get 2 strings from text-box values that have the following ids : startDate and endDate, and convert them to Date objects.

    var start =  document.getElementById ("startDate");
    var end =  document.getElementById ("endDate");
       
    var d1 = convertToDate(start.value);
    var d2 = convertToDate(end.value);

The following statement calculates the difference between 2 Date objects in milliseconds: 

    var span = d2.getTime()- d1.getTime();

Let’s calculate the number of milliseconds in a day:
  
    var day = 1000*60*60*24;

And finally, the representation of the difference in days:

    var days = parseInt(span/day);

Here is a compact generic function by john.ellingsworth that generates a table from a PEAR DB result set. It even uses column names as HTML table column headings.

A hint: to better format a table when there is a null value in the resultset, add a ‘nbsp;’ character to a table cell before a field value.