Home » Technology » JavaScript » Comparing Dates Using JavaScript

Comparing Dates Using JavaScript

© Muhammad Ali Shah

• Level: Basic
• Skills Required: JavaScript Functions

Abstract:

Comparing two dates is a problem general enough to get special attention. When you develop a general purpose solution to such problems, you have a reusable piece of code that can save you hours of time.

Ground Work:

We will write a simple function that takes two well formed dates. The function will compare the dates and return:

• 0 if the dates are same
• -1 if the first one is an earlier date
• 1 if the first one is a later date

We will have to fix the date format. For this tutorial assume it to be mm-dd-yyyy where '-' is a separator. We will make extensive use of three JavaScript methods: substring(start, stop), indexOf(searchString) and lastIndexOf(searchString). They are used to extract a substring out of a string; to find position of a substring in a string and to find the last position of a substring in a string, respectively.

For example, suppose we have "12-10-2000" in the variable value1. To extract the date, month and year parts out of it, we will have to determine the first and last position of hyphen '-'. This can be done quite easily as shown below:

var firstIndex = value1.indexOf ;
var lastIndex = value1.lastIndexOf ;
month1 = value1.substring (0, firstIndex);
date1 = value1.substring (firstIndex+1, lastIndex);
year1 = value1.substring (lastIndex+1, value1.length);

Improving the Code:

There is always room for improvement. Our function assumes that the three parts of the date are separated by a hyphen. This may not always be true. So, it would be better if we pass a the separator string as a third argument to this function. Try this yourself as practice.