Run results for: key in object vs. object[key] === undefined

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36

Browser: Chrome 127

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: one year ago

Test name	Executions per second
Using in keyword	9637754.0 Ops/sec
Using === undefined	3408626.0 Ops/sec

Script Preparation code:

var obj = {a: 5, b: 8};

Tests:

Using in keyword
"a" in obj; "b" in obj; "c" in obj;
Using === undefined
obj["a"] === undefined; obj["b"] === undefined; obj["c"] === undefined;