var prld = ["one.gif", "two.gif", "three.jpg", "..."];
var img = [];
for (i = 0; i < prld.length; i++) {
    img[i] = new Image();
    img[i].src = prld[i];
}

var prld = document.querySelectorAll('img');
var img = [];
for (i = 0; i < prld.length; i++) {
    img[i] = new Image();
    img[i].src = prld[i].src;
}