How to check if BulkOp is empty or not

Working with Data Node.js Frameworks
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4 
// @ts-ignore
if (bulkOp.length >= batchSize) {
	const res = await bulkOp.execute();
...

this is my code, which works. However without the // @ts-ignore, TypeScript generates an error:

Property ‘length’ does not exist on type ‘UnorderedBulkOperation’.

So it ‘thinks’ it doesn’t exist, but in fact it does.