Definitely specific to the V8 JavaScript engine. I was able to put 40 million keys in a map in Firefox/SpiderMonkey. It was pretty fast and only took a few seco

Definitely specific to the V8 JavaScript engine. I was able to put 40 million keys in a map in Firefox/SpiderMonkey. It was pretty fast and only took a few seconds. The pitfall was that because I did it in the Developer Tools console, the CPU and memory usage would shoot through the roof from the autocompleter if I wrote any code that would cause a string representation of the map to be printed as a helpful hint.