CODEWITHSUNDEEP
javascriptobjecthasownproperty
ProllyGeek
ProllyGeek

Reputation: 15836

is there a method equal to hasOwnProperty() that can traverse prototype chain?

for example i have an array , lets call it myArray where :

 var myArray = ['foo', 'bar'];

even though , myArray.join() will return 'foo,bar' , the check myArray.hasOwnProperty('join') , will return false , because simply hasOwnProperty() will not traverse the prototype chain.

Is there a way to do same function with ability to traverse the prototype chain?

P.S : even a custom method will do.

Upvotes: 1

Views: 223

Answers (2)

pwdst
pwdst

Reputation: 13735

If you want to determine if a method or property is available within either the object or within the prototype chain for the object you can use the in operator as cited by elclanrs.

The in operator returns true for properties in the prototype chain.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in

In your example you could write-

if ('join' in myArray) { // do something }

If you want to determine the type of a property within the prototype chain then you can also use the typeof operator. I can't find a "plain English" citation that this works with prototype operators, but if you type the following in the console of the dev tools of your choice-

var myArray = ['foo', 'bar']; typeof(myArray.join);

This will return "function" as expected, demonstrating that this operator does function with prototype functions and properties - and this is something I can also attest to from my experience. The typeof operator will return one of-

"undefined", "object", "boolean", "number", "string"

Upvotes: 1

elclanrs
elclanrs

Reputation: 94101

You can use the in operator.

The in operator returns true for properties in the prototype chain.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in

Like:

if ('join' in myArray) {
  ...
}

Upvotes: 4

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