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

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36

Browser: Chrome 99

Operating system: Windows

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
Using in keyword	4818454.0 Ops/sec
Using === undefined	1695191.0 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;