Arrays Pictues And BackgroundImage

This routine is supposed to change a background with successive images from an array. It worked when I wrote it inline in an html file it worked but having lifted it out I get the error 'missing ) after formal parameters'. What am I doing wrong?

var box ={
init: function(){
box.box = document.getElementById("box");
var mycars = new Array()
mycars[0] = 'url(1.png)'
mycars[1] = 'url(2.png)'
mycars[2] = 'url(3.png)'
mycars[3] = 'url(4.png)'
mycars[4] = 'url(5.png)'
mycars[5] = 'url(6.png)'
box.swap();
},

swap: function(box.box,mycars)
{
for (i=0;i<mycars.length;i++)
{
box.box.style.backgroundImage = mycars[i];
alert("break");
}}};