Javascript String Compare == sometimes fails

Question

How could the following code sometimes evaluate to false?

(transport.responseText == \'1\' || 
 transport.responseText == \'CARD_VALID\')

M

Answer 1

Java servlet may send strings i.e.

out.println("CARD_VALID");

or

out.print("CARD_VALID");

These may look identical in Javascript, but there are white spaces at the end in the first case.