Question

I was trying to debug a sorting issue with the jquery plugin tablesorter which uses the following code to check for digits:

this.isDigit = function(s,config) {
                var DECIMAL = '\\' + config.decimal;
                var exp = '/(^[+]?0(' + DECIMAL +'0+)?$)|(^([-+]?[1-9][0-9]*)$)|(^([-+]?((0?|[1-9][0-9]*)' + DECIMAL +'(0*[1-9][0-9]*)))$)|(^[-+]?[1-9]+[0-9]*' + DECIMAL +'0+$)/';
                return RegExp(exp).test($.trim(s));
            };

the value for config.decimal is ‘.’

Now if s=’0′ this fails, but if you run match instead the RegEx appears to be responding positively as expected.

return exp.match($.trim(s)) != null

How is this processing differently in order to return different results?

Just in case you wanted the HTML where s is derived (The last column is viewed as text):

<tr class="">
  <td><a href="#">Click</a></td>
  <td>Annen Woods</td>
  <td>131</td>
  <td>20</td>        
  <td>5</td>
  <td>3</td>
  <td>12</td>
  <td>6</td>
  <td>50%</td>
  <td>0</td>    
</tr>

I understand that test returns a boolean value and match returns a string or null.

The ultimate question is why isn’t for this regular expression:

return RegExp(exp).test($.trim(s));

equivalent to :

return exp.match($.trim(s)) != null

Answer 1

I think it’s a bit of an odd coincidence due to the function used to construct the regular expression.

Match is a member of String.

Test is a member of RegExp.

However, in the function there, exp is defined as a string. So, technically, you’re running String’s match() using exp as a string value, not as a regular expression.

Running exp through a RegExp constructor should return the same result as test() would.