Run results for: if (!x) syntax vs if (x === undefined)

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36

Browser: Chrome 97

Operating system: Windows

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
"!" syntax	15239805.0 Ops/sec
object.property === undefined	5582312.0 Ops/sec

Script Preparation code:

var obj = {}

AخA
 
var obj = {}

Tests:

"!" syntax
if (!obj["a"]) { return false };
if (!obj["a"]) { return false };
object.property === undefined
if (obj["a"] === undefined) { return false };
if (obj["a"] === undefined) { return false };