Benchmark: conditional self-assignment vs. membership check with in vs. membership check with hasOwnProperty vs. null check

Script Preparation code:

var x = {
    foo: []
};
var keys = Array.from({
    length: 5000
}).map((x, i) => i < 2500 ? i : i - 2500);

Tests:

hasOwnProperty membership check
for (const key of keys) { if (!Object.prototype.hasOwnProperty.call(x, key)) { x[key] = []; } }
self-assignment
for (const key of keys) { x[key] = x[key] ?? []; }
in membership check
for (const key of keys) { if (!(key in x)) { x[key] = []; } }
null check
for (const key of keys) { if (x[key] == null) { x[key] = []; } }

Rendered benchmark preparation results:

Previous results

Test case name	Result
hasOwnProperty membership check
self-assignment
in membership check
null check

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Latest run results:

Run details: (Test run date: 10 months ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36

Browser/OS: Chrome 114 on Mac OS X 10.15.7

Test name	Executions per second
hasOwnProperty membership check	2069.3 Ops/sec
self-assignment	2920.5 Ops/sec
in membership check	6152.3 Ops/sec
null check	5753.1 Ops/sec

conditional self-assignment vs. membership check with in vs. membership check with hasOwnProperty vs. null check (version: 0)