2. Prefetch Images I
	“Prefetch” means to get the images and save them in (our own) array so they are handy to assign to doc.im • We must declare an array (and probably an index variable, too):    var i, pref = new Array(4); • Then we set it up to hold images:    for (i=0; i<4; i++) {      pref[i] = new Image;    }