Question

function ReplaceContentInContainer(matchClass,content)
    {
    var elems = document.getElementsByTagName('*'), i;
    for (i in elems)
        {
        if((" "+elems[i].className+" ").indexOf(" "+matchClass+" ") > -1)
            {
            elems[i].innerHTML = content;
            }
        }
    }

I’m trying to figure out what the comma does in the variable assignment ('*'), i;
and what that means in the for (i in e) loop.

My best guess is that e is assigned to both all the elements in the document node as well as i. So does that mean that i is a count or reference of the number of elements in the array e (is it an array?)?

edit:
Okay. It’s just instantiating the variable (i) and then i, in the for loop, counts all the elements in the object elem.

Answer 1

That simply separate the declarations.

var elems = document.getElementsByTagName('*'), i;

is the same as

var elems = document.getElementsByTagName('*');
var i;

One is more concise, the other one might be seen as more readable.

In your precise case, you could have used

var elems = document.getElementsByTagName('*');
for (var i in elems)

which would be, in my opinion, the best as the purpose of i would have been obvious.

As the scope of a variable is the function (or global) and not the block, it would have been exactly identical.