the batiks i've seen from Joannes DO BLEED AND SHRINK! be sure and at least test before using. if you are leaning toward not prewashing a test should be done...
quality does make a huge difference in the properties of batiks, joannes batiks are nothing like hoffman bali batiks. all batiks should be tested for color fastness. and the ones dyed on (less expensive) looser weaved fabrics will shrink along with bleeding.
ALWAYS BETTER TO BE SAFE THAN SORRY.