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The Javascript Garbage Collector

When you program programs in Javascript, we ceaselessly “disregard” the reminiscence intake, depending at the “magical” skill of the browser (or working machine, relying at the context of the application – see Node.js) to deal with it. In truth this isn’t all the time so, and for extra advanced programs occur to having to invite how it’s treated this side.

By following one of the concepts that was once mentioned in a publish by way of Steve Hanov, it’s conceivable to test if a Javascript object has been “destroyed” (after which got rid of from reminiscence) by way of the rubbish collector of the browser. Unfortunately, the process works with Chrome and different browser however no longer with Firefox. Nevertheless, it stays a useful gizmo to check and debug.

The code

The following code makes use of the category WeakMap to map 1 GB of reminiscence to some other object. In the instant during which the latter is deleted by way of the rubbish collector, they’ll additionally take away the GB related to it. Exploiting the likelihood (presented by way of Chrome) to test the quantity of reminiscence used, it’s conceivable to research if the article that we’re keen on analyze has been freed or no longer.

In addition to the above, you’ll realize the presence of a time-out this is appearing each and every 10 seconds. The reason for that is because of the truth that Chrome runs the rubbish collector to roughly common durations, simply 10 seconds.


/** Determines if an object is freed
@param obj is the article of passion
@param freeFn is a serve as that frees the article.
@returns a promise that resolves to {freed: boolean, memoryDiff:quantity}
@writer Steve Hanov <[email protected]>
*/
serve as isObjectFreed(obj, freeFn) { go back new Promise( (get to the bottom of) => { if (!efficiency.reminiscence) { throw new Error("Browser no longer supported.");
} // When obj is GC'd, the massive array may also be the GCd and the have an effect on will // be noticeable. const allocSize = 1024*1024*1024; const wm = new WeakMap([[obj, new Uint8Array(allocSize)]]); // look ahead to the reminiscence counter to replace setTimeout( () => { const ahead of = efficiency.reminiscence.usedJSHeapSize; // Free the reminiscence
freeFn(); // look ahead to GC to run, no less than 10 seconds setTimeout( () => { const diff = ahead of - efficiency.reminiscence.usedJSHeapSize; get to the bottom of({ freed: diff >= allocSize, memoryDiff: diff - allocSize
}); }, 10000); }, 100);
});
}
let foo = {bar:1};
isObjectFreed(foo, () => foo = null).then( (end result) => { file.write ("Object GCd:${end result.freed}, ${end result.memoryDiff} bytes ' freed`)
}, (error) => { file.write(`Error: ${error.message}`)
})

The binding of 1 GB of reminiscence to the article to be analyzed, is born from the desire as a way to check an important distinction within the quantity of reminiscence used. Without this “trick”, the adaptation would no longer be vital, and the research of reminiscence can be difficult (if no longer inconceivable).

It is plain to notice that it’s under no circumstances the perfect “waste” 1 GB of reminiscence in a manufacturing setting. However, the one you’ve simply noticed stays an invaluable instance acceptable within the section of trying out and debugging, particularly for programs that use items which are arduous to regulate, “immersed” within the framework comparable to React, Vue.js or Angular.

Source: Steve Hanov