Really bad use of javascript can cause a memory leak in browser.
Garbage collection != memory leak proof
The problem with downvotes in HN is the side effects. An early downvote can mean nothing more significant than "I disagree with you", but it has the effect of making a post significantly harder to read. When a post is hard to read, fewer people will read the post, yet they are willing to accept and re-enforce the judgement of their peers (especially HN personalities) without critically reviewing it for themselves.
I wouldn't personally blame Jacques for this, but his dismissal (and possibly the early downvote as well) has had a net negative effect on the OP, regardless of the OP's correctness.
EDIT: And our sin appears to be getting too meta. Cardinal sin, that.
So let's say this 'terrible' javascript page allocates 2G of RAM. If you refresh the page and the memory stays allocated that is a memory leak. But if it frees it and then reallocates it then it is not a memory leak but just working as designed to (as is your example above).
Memory leaks are not properties of websites but properties (or rather hopefully not) of browsers indicating a bug in the browsers code, no website should be able to cause a browser to leak memory and if such websites can be found bugs should be logged against those browsers that can be reproducibly caused to lose track of their memory allocation.
It's not all that hard.