Question

I am learning about DOM collections. The textbook I’m using had the following Javascript code for iterating through the elements of the links collection:

var linksList = document.links;
for (var i = 0; i < linksList.length; ++i)
{
    ...
    [code to print links to HTML paragraph]
    ...
}

Just for fun I changed the loop to a for ... in style loop:

for (var i in linksList)

and afterwards noticed that my script was now generating 3 more links than before, and each of them was “undefined.”

1) What are these undefined links, and why are they accounted for in a for ... in loop, but not the loop governed by document.links.length? (obviously length is 3 shorter than “true” length which includes the 3 mystery links)

2) How do I view collection using developer tools? If I could do this, perhaps I could answer the previous question myself.

Thanks!

Answer 1

Actually, document.links returns an array-like object, that while providing length property and supporting indexing, has other properties, that show up in for in loop.