Ok... looks like somebody doesn't handle string quoting at all. So what should I do now ? Contact them to fix this bug ? No. I hit the "shell bookmarklet" that has always been there on my Firefox personal toolbar, and type:
add_to_cart('3729',"I'm a Mac (XL號)",'399',myform.buy_number_3729_2)
Right, just change the bad string in the second argument to use double quote, and call that function. Alrighty, now the T-shirt is in my cart!
Ponder, didn't they ever wondering why the T-shirt doesn't sell as well as it should be ?