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

Run details:

User agent: Mozilla/5.0 (X11; Linux x86_64; rv:131.0) Gecko/20100101 Firefox/131.0

Browser: Firefox 131

Operating system: Linux

Device Platform: Desktop

Date tested: one year ago

Benchmark engine: Benchmark.js

Using === undefined

1797.8M/s

Using in keyword

1642.0M/s

View exact numbers

Test name	Executions per second
✓ Using === undefined	1,797,822,208 Ops/sec
Using in keyword	1,642,023,296 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;