Applying Masks Using Regular Expressions In Javascript

I have blogged several times about using regular expressions (RegExp) in Javascript. I think regular expressions are absolutely wonderful. And, one of the great things about Javascript regular expressions (as opposed to reg ex in other languages) is that you can pass the individual groups matches to a function call:

This is a really cool feature, but it was not until recently that I came to see the amazing POWER of this feature. I am working on a prototype library of useful functions such as string trimming and date formatting. Date and time formatting, as you might know from ColdFusion, takes a mask argument to define how the date should be formatted. For example, the mask "mm/dd/yyyy" would return the string "08/01/2006".

There are many different combinations of masks available to the user. As it turns out, using this regular expression flexibility, it actually makes applying a mask extremely easy. To explore this, let's take a look at my formatDate() function:

The first thing I do inside the formatDate() function is define the values for each part of the potential mask:

Each part of the object (equivalent to a ColdFusion struct), objPart, is a possible part of the date mask. Now, assuming that the passed argument "strMask" holds the user's desired date format, we could apply the mask to the date using regular expression:

As you can see, the regular expression (d{1,4}|m{1,4}|y{4}|y{2}) will simply match any possible part of the available date mask options. Each matching part is then passed to the function we defined as the second argument to the replace() method. This function merely returns the value of the objParts[] object using the matched group as the key. Take a second to sit back and be in awe of the amazing flexibility that this allows you.

Putting it all together:

Can you imagine trying to do this without regular expressions? Let's take a look at an example that doesn't use regular expression. This example was taken off of the Javascript Tool Box:

While the code is hard to read (I wasn't about to take the time to parse it), you can clearly see that there are multiple WHILE loops. And within each of those while loops they are getting tokens, performing logic, checking for null values. All a complete waste of time. Let Javascript perform the heavy lifting for you.

Are you beginning to see the possibilities? Regular expressions are so freakin' powerful it almost makes my ears bleed to think about it.

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