Issue solved

Shall we close the issue then?

I made it clearer now I believe. I also included an image.

If this is no longer an issue could you mark as solved please? Thank you.

Description modified.

totally agree ! Damn...

String.prototype.search (e.g. in this example there's an abc2.search) expects a regular expression as a parameter, even though str.charAt(i) is not always a valid regular expression.

You're not even up to the random tests. I'm assuming from your output that you're constructing a regular expression via a string without escaping regular expression syntax. Unfortunately there's no native way in Javascript to do that. You could do it with a full knowledge of Javascript regular expressions, although JS regexps could change in the future which could make it a maintenance issue. You might want to change your approach.