After a long time fighting with this problem, I think I have found a better solution.
The combination of two functions makes it possible to escape a string to use as HTML.
One, to escape double quote if you use the string inside a JavaScript function call; and a second one to escape the single quote, avoiding those simple quotes that go around the argument.
Solution:
mysql_real_escape_string(htmlspecialchars($string))
Solve:
echo 'onclick="javascript_function(\'' . mysql_real_escape_string(htmlspecialchars($string))"