Question

While converting an old code, I encountered the following problem.

Given an HTML string,

   <Font face="Arial" size="21" color="#000000"> 
     THIS IS SIZE 21    
    </Font>

I want to subtract a factor “X” from the size “21” in the output string by using Regex?

So the new string be

   <Font face="Arial" size="(21-X)" color="#000000"> 
     THIS IS SIZE (21-X)    
    </Font>

Example

Original String

   <Font face="Arial" size="21" color="#000000"> 
     THIS IS SIZE 21    
    </Font>

and factor = 8 (so subtract 8 from size ..so new size = 21- 8 =13 )

Output String

   <Font face="Arial" size="13" color="#000000"> 
     THIS IS SIZE 13   
    </Font>

Can this type of processing be done using Regex.
Something similar to match evaluator in C#

Whats the best way to do this sort of conversions??

Answer 1

Try something like the following:

var html = '<Font face="Arial" size="21" color="#000000">\n' +
           '  THIS IS SIZE 21 \n' +
           '</Font>';
var factor = 8;
html = html.replace(/(size=")(\d+)(")/g, function(m, c1, c2, c3) { 
    return c1+(c2-factor)+c3; 
});

The function gets called with the first argument being the full match, followed by the captures. Its return value is used to replace the match inside the result.