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Which is faster: obj.hasOwnProperty(prop) vs Object.keys(obj).includes(prop)

Ethan Arrowood
Microsoft Software Engineer
・1 min read

I don't know how to test runtime speed but I'm interested in which of these methods would cause more overhead.

Given an object with n properties (also called keys) is it faster to check if that property exists using obj.hasOwnProperty(prop) or Object.keys(obj).includes(prop). Something to consider is what if you need to check multiple properties multiple times?

If you store the keys in a variable: const keys = Object.keys(obj) and then make a series of checks keys.includes(prop1); keys.includes(prop2); is this faster or slower than obj.hasOwnProperty(prop1); obj.hasOwnProperty(prop2);

Discussion (6)

ycmjason profile image
Jason Yu • Edited

I bet it has to be Object.hasOwnProperty.

Depending on the runtime implementation, Object in JavaScript should be somewhat similar to a HashMap. So a key lookup should be O(1). Array.includes on the other hand is obviously O(n). They really are not very comparable.

Object.hasOwnProperty would be more comparable to the in operator. in should be a little bit more complicated as it looks through the prototype chain as well. But for keys that are already attached to an Object, I suppose it should give a similar, if not the same, time complexity.

ethanarrowood profile image
Ethan Arrowood Author • Edited

Turns out the Array includes method is faster!

ycmjason profile image
Jason Yu

Try a bigger object, say with 20000 keys.

ycmjason profile image
Jason Yu

interesting, is this running on node?

varoman profile image
varo manukyan

I like testing execution time with console.time(string) and console.timeEnd(string).

Though, as one could guess testing performance this way is a fail. It will give various results every time. You'd better use developer tools instead.

Anyway, Object.hasOwnProperty compared to prop in obj should be incredibly faster as the latter run through all the prototype chain of an object. I've run that tests on small objects and get what I expected.

rhymes profile image

Maybe you can find out with ?