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// hasOwnProperty approach for (key in obj) { if (obj.hasOwnProperty(key)) { value = obj[key]; } } // Object.keys approach keys = Object.keys(obj); for (i = 0, l = keys.length; i < l; i++) { value = obj[keys[i]]; } According to jsperf the Object.keys approach is 50%+ faster http://jsperf.com/object-keys-vs-hasownproperty/45
Why is this?
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hasOwnProperty() is faster. I realize there are other ways to make the loops faster, like storing lengths in variables.
So what's the difference between the two? The key difference is that in will return true for inherited properties, whereas hasOwnProperty() will return false for inherited properties.
hasOwnProperty() should be O(1) , as it is a key lookup, but it will be implementation specific.
Conclusion. It turns out that Object. values is about 3.2 times faster than Object.
Object.keys looks up all own, enumerable properties (oh, and arrays are fast).for in additionally looks up inherited enumerable properties, not only own onesfor in + hasOwnProperty additionally tests all looked up properties for whether they are own properties.Even if there are no inherited enumerable properties, it is still more work to do than not.
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