CODEWITHSUNDEEP
javascript
ILikeTacos
ILikeTacos

Reputation: 18666

In JavaScript, what is the purpose of self-calling `call`?

I'm maintaining a javascript library whose original author is not longer working at the company.

I've found the following pattern repeated across the library:

 var events = {}; // defined globally

 // many lines below within a function:
 if(!events.hasOwnProperty.call(events, eventKey)) return;

Does the use of call in that way offer any technical advantage over just doing:

if (!events.hasOwnProperty(eventKey)) return;

I feel like the former is less intuitive than the latter, and the latter is more expressive assuming the output is identical

Upvotes: 0

Views: 45

Answers (1)

philipp
philipp

Reputation: 16515

Both are the same! There is no diffrerence. Any Object {} has the method hasOwnProperty() (Object.prototype.hasOwnProperty), what is a function (or function object) and any function (-object) has a method call() (Function.prototype.call) mdn-docs

And the first argument of Function.prototype.call() is the »this context/object«, or context/sidecar/this/that/etc…

So, in your case: events.hasOwnProperty.call(events, …) is just the very same as events.hasOwnProperty(…), since in the first case events will be this, because it was used as first argument to call(). In the latter case, events will also be this, since JS will always set the context/this automatically on each objects' method, if you do obj.method().

Or in code:

var 
  A = { log: console.log(this) },
  B = {};

A.log() // A
A.log.call(A) // A

A.log.call(B) // B

Upvotes: 1

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