Map - JavaScript | MDN
6
Public whispers
6
Contributors
2026-07-18 09:45:38
First whispered
Public whispers on this page
Text Highlight2026-07-18 16:09:38
Original Highlight Excerpt
"the data itself is not cloned."
Whisper Note
Wait, so if I mutate the object inside the map, the original changes too? That's kinda scary.
Text Highlight2026-07-18 13:06:38
Original Highlight Excerpt
"Maps can be iterated using a for...of loop"
Whisper Note
Is that any different from iterating an object? Seems obvious.
Text Highlight2026-07-18 12:57:38
Original Highlight Excerpt
"Maps can be iterated using a for...of loop"
Whisper Note
Yeah, for...of works fine but I always forget the destructuring syntax.
Text Highlight2026-07-18 10:03:38
Original Highlight Excerpt
"NaN can also be used as a key."
Whisper Note
So it's like a black hole key, everything NaN just collapses into one.
Text Highlight2026-07-18 09:54:38
Original Highlight Excerpt
"NaN can also be used as a key."
Whisper Note
I've been avoiding NaN as a key for nothing, good to know.
Text Highlight2026-07-18 09:45:38
Original Highlight Excerpt
"NaN can also be used as a key."
Whisper Note
Wait, so NaN keys actually work? That's wild.
Share this page's whispers
Short link
https://domwhisper.com/s/c6ceb1b3cc7fEmbed snippet
<iframe src="https://domwhisper.com/embed/c6ceb1b3cc7f" width="100%" height="480" style="border:0;border-radius:16px" loading="lazy"></iframe>See what people are discussing on developer.mozilla.org
Install DomWhisper to view live whispers as you browse, and join the discussion.
Get the extension