Check if a property exists in an object

Comments

[Federico Vázquez]

Depends on what you need, but I'd say

({test: undefined}).hasOwnProperty('test')

is better.

They don't produce the same result, since the in operator is going to search for that property in the entire prototype chain, while hasOwnProperty is going to look for that prop only in the context of that object.

[Mehul Lakhanpal]

Nice I didn't know that 'in looks up the chain. Good to know :)

[Federico Vázquez]

You're right. I assumed in was slower simply because it has to iterate many levels, but looks like currently V8 knows how to properly optimize the loop. Thanks for pointing out, I'll edit that part.