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

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/114.0

Browser: Firefox 114

Operating system: Windows

Device Platform: Desktop

Date tested: 10 months ago

Test name	Executions per second
Using in keyword	753551900.0 Ops/sec
Using === undefined	728456300.0 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;