gistfile1.js

/**
 * Check wether the given ``answer`` produces the right output for 
 * the current level.
 *
 * Returns ``null`` on success. Otherwise returns the wrong output.
 */
Soret.check_answer = function(regex, repl) {
    var user_output = Soret.sub(regex, repl);
    if (user_output != Soret.get_expected_output())
        return user_output;
    return null;
};