Potash Valley

Today I needed to create a mass email sender application for a customer, in order to warn the users of their personal data. The template had some complexity like loops for multi-valued information, thus I needed a template engine.

The goal was to have a text processor which could take an external object model (actually a CSV file) and a template file like ASP.NET does:

Dear <%= firstname %> <%= lastname %>,

This is a set of squares:
<% for (var i=0; i<3; i++) { %> 
    <%= i %> * <%= i %> = <%= i * i %> 
<% } %>

Regards

And the result should look like this:

Dear Sébatien Ros,
This is a set of squares:
0 * 0 = 0
1 * 1 = 1
2 * 2 = 4

Regards

I quickly searched for this sort of tool when I wondered how they would be made. Actually ASP.NET changes the ASPX file into code files which is I suppose the best approach. The only thing I needed was a way to execute this generated code. And guess what, I already have it, it's Jint, again ;)

So the only thing to do is use a simple state machine and a regular expression to convert the previous template to this script :

write('Dear '); write( firstname ); write(' '); write( lastname ); 

write(',\r\n\r\nThis is a set of squares:\r\n');  
for (var i=0; i<3; i++) { 
    write(' \r\n    '); 
    write( i ); 
    write(' * '); 
    write( i ); 
    write(' = '); 
    write( i * i ); 
    write(' \r\n');  
} 

write('\r\n\r\nRegards'); 

I also configured Jint so that the write method appends its parameter to a local StringBuilder instance, and took all variables like firstname and lastname to declare them locally in the script. Then I ran the script using Jint and emailed the resulting string to the recipient.

I'm sure I will find even more usages for Jint in the future.