Symbol not getting removed when item is removed from tree

[Ineluki]

When items are repeatedly added to and removed from new trees, the symbols stay and start clogging up the memory. Don't know if this is necessary by design or not.

My simple test:

const SymbolTree = require('symbol-tree');

const base = [];
for(let i=0; i<100; i++) {
	base.push({ content: i });
}

for(let i=0; i<1000; i++) {
	let tree = new SymbolTree();
	let root = { root: true };
	base.forEach(obj => {
		tree.appendChild(root, obj);
	});

	let it = tree.childrenIterator(root);
	for( child of it ){
		tree.remove(child);
	}
	console.log(JSON.stringify(process.memoryUsage()));

}

[Joris-van-der-Wel]

This was indeed by design because it was the fastest solution for jsdom's use case. In jsdom objects are often removed from the SymbolTree and then added back a little while later. (Also note that jsdom uses a finite amount of SymbolTree instances). Deleting and then adding back the property would be slower, and also delete may cause deopts in v8.

Would it help if I added an option to the constructor?

const tree = new SymbolTree({cleanup: true});
tree.remove(someObj); // which would then trigger `delete someObj[this.symbol]`

And then jsdom could continue to use the {cleanup: false} behaviour.

[Ineluki]

That would be a good solution, yes. If delete is bad in these cases, I'd just recommend setting it to null if that makes a difference. But if it's by design, don't feel pressured on my part. Turns out I can't use this awesome lib anyway, unfortunately, since it can't allow the same object multiple times. Just thought I'd mention the problem since I already wrote the test and thought somebody might one day run into the problem ;)