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I've just read that WeakMaps take advantage of garbage collection by working exclusively with objects as keys, and that assigning an object to null is equivalent to delete it:

let planet1 = {name: 'Coruscant', city: 'Galactic City'};
let planet2 = {name: 'Tatooine', city: 'Mos Eisley'};
let planet3 = {name: 'Kashyyyk', city: 'Rwookrrorro'};

const lore = new WeakMap();
lore.set(planet1, true);
lore.set(planet2, true);
lore.set(planet3, true);
console.log(lore); // output: WeakMap {{…} => true, {…} => true, {…} => true}

Then I set the object equal to null: 

planet1 = null;
console.log(lore); // output: WeakMap {{…} => true, {…} => true, {…} => true}

Why is the output the same? Wasn't it supposed to be deleted so that the gc could reuse the memory previously occupied later in the app? I would appreciate any clarification. Thanks!

Bruno Mazza
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    "*assigning an object to null is equivalent to delete it*" - no, removing the reference from your variable does make the object *eligible* for garbage collection (when that happens). It does not immediately delete anything. – Bergi Apr 15 '18 at 12:55
  • https://stackoverflow.com/questions/38203446/javascript-weakmap-keep-referencing-gced-objects – Bergi Apr 15 '18 at 12:58
  • Also, these things will all get garbage collected as soon as GC runs since WeakMap doesn't retain a reference to the object. You need to store references to the planets somewhere else or the WeakMap will immediately throw them away. – podperson Feb 25 '21 at 22:43

1 Answers1

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Garbage collection does not run immediately. If you want your example to work you need to force your browser to run garbage collection.

Run chrome with the following flag: google-chrome --js-flags="--expose-gc".

You can now force the garbage collection by calling the global gc() method.

enter image description here

Tomasz Kula
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