Discussion on: JavaScript check if property exists in Object

[Supportic]

You could also do if(userOne["email"]) but I would not recommend to check like this userOne.email !== undefined because what if the object in general does not exist?

if ({} !== undefined) true
=> true

if (undefined !== undefined) true
=> undefined

means:
When userOne does not exist e.g. you forget to pass parameter in a function call, then (undefined).email !== undefined will evaluate not into false or true

undefined && true
=> undefined
undefined && false
=> undefined

=> skip if condition

A fix for that though would be to check if the object exist and if not, assign an empty object to it.
options = options ?? {}
if (options.switch !== undefined) can now resolve in true or false.

[Chris Bongers]

Yeah that's why I mentioned the undefined check to be the least favorite one of all.
It get's messy and very prone to cause headaches later on.

[peerreynders]

what if the object in general does not exist?

As suggested in another comment optional chaining will work just fine here.

const options = undefined;
console.log(options?.email ? true : false); // false
// i.e. No Uncaught ReferenceError 
// even though options is `undefined`