javascript - Why delete operator returns true even if property wasn't deleted from an object

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    par.a

, it returns true and actually deletes the property, but it also deletes


    ch.a

. Why? Because using


    Object.create

you just create a reference to the object, not a new copy. Here is a very good article about


    delete

: perfectionkills.com/understanding-delete -- you can read the behaviour of


    Object.create

from here - MDN – Niccolò Campolungo Sep 7, 2013 at 17:44

Throws in strict mode if the property is an own non-configurable property (returns false in non-strict). Returns true in all other cases. ( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete )

delete ch.a tries to locate the property a in ch , fails (since ch doesn't have such own property), does nothing and happily returns true . If you wrote delete ch.foobar , the result would be the same. If however, you tried a non-configurable property (e.g. delete ch.__proto__ ), the result would be false .

I think ch has property ch.a (1) and in this case it is inhereted, and I know it. But I just expect if I don't know if property is inhereted to get false if it didn't deleted. – Andrew Sep 7, 2013 at 18:12 @ruan65:


    delete

only returns


    false

if you're not allowed to delete a property, and


    true

in all other cases - no matter if a property was actually deleted or not. – georg Sep 7, 2013 at 20:36 this was poor implementation/specification - it should THROW if you are not allowed to delete the property, return false, if the property does not exist, and return true if the property exists. To be even more precise, in strict mode, it should throw if it's non-configurable, o/w return false if it's non-configurable. – Alexander Mills May 26, 2018 at 21:07

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