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/605.1.15 (KHTML, like Gecko) Version/17.1 Safari/605.1.15

Browser: Safari 17

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
Using in keyword	4940678.5 Ops/sec
Using === undefined	2311877.2 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;