javascript - for-in vs Object.keys forEach without inherited properties

Question

I was looking at a perf benchmark of Object.keys + forEach vs for-in with normal objects.

This benchmark shows that Object.keys + forEach is 62% slower than the for-in approach. But what if you don't want to get the inherited properties? for-in includes all non-native inherited objects, so we'll have to use hasOwnProperty to check.

I tried to make another benchmark here doing exactly that. But now the for-in approach is 41% slower than Object.keys + forEach.

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update

The above test was done in Chrome. Tested it again but with Safari and I'm getting different results: Object.keys(..).forEach(..) 34% slower, odd.

Note: The reason I'm benchmarking is to check how it is with Node.js.

Questions:

• Are the jsperf result for Chrome considerable for Node.js?
• What happened, how come a single conditional made the for-in approach 41% slower than Object.keys + forEach in Chrome?

Answer 1

node.js uses V8, although I guess it's not the same as the current version in Chrome, but I guess it's a good indicator of node's performances on the subject.

Secondarily, you're using forEach, which is quite handy when developing but adds a callback for every iteration, and that's a (relatively) lenghty task. So, if you're interested in performances, why don't you just use a normal for loop?

for (var i = 0, keys = Object.keys(object); i < keys.length; i++) {
    // ...
}

This yields the best performances you can get, solving your speed problems in Safari too.

In short: it's not the conditional, it's the call to hasOwnProperty that makes a difference. You're doing a function call at every iteration, so that's why for...in becomes slower.