passing values and variables

i've error in this code:
Error:'document.images[...]' is not an object

var state=1;
function animate1(img) {
 document.images[img].src=downImage[0].src;
 if(state==1) setTimeout("animate2()",99);
 }
function animate2(img) {
 document.images[img].src=defaultImage[0].src;
 if(state==1) setTimeout("animate1()",99);
 }

i pass 'img' parameter when onMouseOver="rollImage('image1', 'over');
this attribute is attached to name="image1" of the document image.
function rollImage(img, type) {
 switch(type) {
  case "over":
   state="1";
   animate1(img);
   animate2(img);
   break;
  case "out":
   state="0";
   document.images[img].src=defaultImage[0].src;
   break;
  case "down":
   state="0";
   document.images[img].src=downImage[0].src;
   break;
  }

problem is that combination of above3functions not working.
error in arguments passing problem ?
but if we use 'document.writeln(img);' in functions animate1()
and animate2() we get right value 'image1' on screen.
also if we use 'document.images['image1'].src' or
'document.images["image1"].src' in these both functions above,
this code works fine. also if i've spelled 'image1' as image in
'document.images[image1].src' there is the same error i've said
in beginning in this post.

but i've2pass image_name to animate1() and animate2() via
rollImage() because i've >1 images in my document:
name="image1", name="image2", ....., name="image9", .., etc.
could i solve this argument-variable passing problem ?
u c that i tranmit a variable ( that contains some value )
through functions.

and code shown below works just fine: [Sun rises in the east.]
function a(a) {
 a+=" rises";
 b(a);
 }
function b(b) {
 b+=" in the east";
 document.writeln(b);
 }
function c(c) { a(c); }
var text="Sun";
c(text);
so what wrong i did with document ( DOM ) variables ?

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You aren't passing any values in the setTimeout calls:

setTimeout("animate2()",99);

should be:

setTimeout("animate2(img)",99);

HTH,

Snib

<><

no that is not working.
actually i think i m not able2(transmit/transit) DOM variables containing values from one function2another in that functions.

.. but why document.writeln(img); outputs as if values are passed ..

also if i put constant values like 'image1', 'image2'
in this code without any suggested modification like
{setTimeout("animate2('image1')",99);}, these functions works. DOM values are not getting into functions correctly ?

can anyone list few urls that explain exhaustive/comprehensive information about javascript functions. i couldn't find this at sites like javascriptkit.com, dynamicdrive.com etc.

if some of u've this problem as i'd, u can solve it simply using javascript in-built eval() function.