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

Run details:

User agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36

Browser: Chrome 126

Operating system: Linux

Device Platform: Desktop

Date tested: one year ago

Benchmark engine: Benchmark.js

Using in keyword

6.1M/s

Using === undefined

2.1M/s

View exact numbers

Test name	Executions per second
✓ Using in keyword	6,116,487 Ops/sec
Using === undefined	2,099,098 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;