Is there an ES6+ alternative to doing Object.prototype.hasOwnProperty.call(obj, key)?

Question

The most bulletproof way of checking if an object has a certain key is:

Object.prototype.hasOwnProperty.call(obj, key)

This provides certain guarantees: it will only evaluate to true if key is a direct property of obj, and it will work even if obj doesn't have the usual Object as its prototype (for example, if it was created with const obj = Object.create(null)).

But it's a mouthful.

Is there any new syntax/method in ES6 or higher (including polyfillable or Babel-compilable 'proposals') that gives the same guarantees, but in a nicer, more readable way?

Why not just alias it with a variable? i.e. const iHaz = Object.prototype.hasOwnProperty then use it like const iDoHaz = iHaz.call(obj, key) — Joseph
– Joseph, Commented Jul 20, 2017 at 13:11
Well, given that you almost never need to use this, what's the problem? — Bergi
– Bergi, Commented Jul 20, 2017 at 13:13
const has = (obj, prop) => Object.prototype.hasOwnProperty.call(obj, prop) is the alias I typically use. — zzzzBov
– zzzzBov, Commented Jul 20, 2017 at 13:16
The only ES Next feature I can think of that would shorten this at all is the bind operator, and its not much of a win here: obj::Object.prototype.hasOwnProperty(key). — Jared Smith
– Jared Smith, Commented Jul 20, 2017 at 13:20
@callum actually I guess you could combine that with Bergi's answer and get obj::({}).hasOwnProperty(key) but that's a lose in terms of readability and I'm not sure how the precedence works out or even if the precedence for the bind operator proposal has stabilized. — Jared Smith
– Jared Smith, Commented Jul 20, 2017 at 13:23

Bergi · Accepted Answer · 2023-01-30 17:08:23Z

14

Update: Object.hasOwn(obj, key) is part of ES2022.

I'm not aware of any syntactical sugar for this. But you shouldn't need to use this very often¹, so writing it out occasionally shouldn't be too bad. An equivalent shorter version would be

({}).hasOwnProperty.call(obj, key)

If you really need to use it more often, just define a helper function:

const hasOwn = (obj, key) => Object.prototype.hasOwnProperty.call(obj, key);
const hasOwn = Function.prototype.call.bind(Object.prototype.hasOwnProperty);

_{1: In most cases, you can omit the check, use in instead, or should be using a Map with its comfortable has method.}

edited Jan 30, 2023 at 17:08

answered Jul 20, 2017 at 13:21

Bergi

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double-beep · Accepted Answer · 2021-12-29 12:16:57Z

5

Object.hasOwn was added to Object standard API. It is now supported on all major browsers.

edited Dec 29, 2021 at 12:16

double-beep

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answered Aug 12, 2021 at 15:30

Fabiano Taioli

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2 Comments

Arzet Ro Over a year ago

Not supported on Safari except Desktop Safari Technical Preview. But it can be polyfilled.

Abel Wenning Over a year ago

Safari desktop and iOS added it March 2022. Edge & Firefox added it September 2021.

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