javascript - What are ECMAScript 6 WeakMaps? -

after reading description: http://wiki.ecmascript.org/doku.php?id=harmony:weak_maps

i'm trying hang of it, not overall picture. about? seems supported in firefox 6: http://kangax.github.com/es5-compat-table/non-standard/

weakmap

weakmaps allow have hashtable key isn't string.

so can set key be, i.e. [1] , can map.get([1])

example mdn:

var wm1 = new weakmap(),     wm2 = new weakmap(); var o1 = {},     o2 = function(){},     o3 = window;  wm1.set(o1, 37); wm1.set(o2, "azerty"); wm2.set(o1, o2); // value can anything, including object or function wm2.set(o3, undefined); wm2.set(wm1, wm2); // keys , values can objects. weakmaps!  wm1.get(o2); // "azerty" wm2.get(o2); // undefined, because there no value o2 on wm2 wm2.get(o3); // undefined, because set value  wm1.has(o2); // true wm2.has(o2); // false wm2.has(o3); // true (even if value 'undefined')  wm1.has(o1);   // true wm1.delete(o1); wm1.has(o1);   // false 

the reason existance is:

in order fix memory leak present in many uses of weak-key tables.

apparently emulating weakmaps causes memory leaks. don't know details of memory leaks.