Passing Argument to JavaScript Object Getter

Question

var URIController = {
    get href() {
        return url.location.href;
    }
}

I have above object structure. But URIController.href property depends on another object, url.

If the url is defined globally, URIController.href works. But I want to pass url object to href getter manually.

var URIController = {
    get href(url) {
        return url.location.href;
    }
}

Changed the getter to accept url parameter but

URIController.href(url)

throws error because href is not a function.

Is it possible to pass arguments to getter in javascript?

AFAIK it's not possible to pass args to a getter in any language, you'd either have to use a "normal" function or introduce a dependency — Paul S.
– Paul S., Commented May 21, 2016 at 17:46
@PaulS. Well... there's at least one language that allows it... — jrh
– jrh, Commented Dec 26, 2018 at 23:26

sdgluck · Accepted Answer · 2024-09-11 15:11:46Z

30

Getters do not require explicit invocation with parentheses and cannot therefore accept arguments. Their invocation is implicit via standard property access syntax, e.g. just URIController.href instead of URIController.href().

From getter documentation on MDN:

The get syntax binds an object property to a function...

It must have exactly zero parameters

______

If you need to accept arguments, use a function instead:

const URIController = {
    href (url) {
        return url.location.href;
    }
}

edited Sep 11, 2024 at 15:11

answered May 21, 2016 at 17:43

sdgluck

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2 Comments

John Bernard Over a year ago

This was actually a library. I just thought if I could modify getter a bit, I can help myself without replacing all properties with function calls in library. But it seems it is not possible.

Jemar Jones Over a year ago

@JohnBernard I know you've probably figured this out by now, but a note to others: for the 'getter' to receive the url parameter whenever used in the library, you'd have to modify each usage of the getter anyway.

Patrick Evans · Accepted Answer · 2016-05-21 18:09:22Z

As per the spec

The production PropertyAssignment : get PropertyName ( ) { FunctionBody } is evaluated as follows:

...

Let closure be the result of creating a new Function object as specified in 13.2 with an empty parameter list and body specified by FunctionBody.

So you cannot specify a parameter list, attempting to do so will give you a syntax error

var obj = {
    get href(param){}     
}

If you do not want to setup a normal function you could do a couple workarounds like set a property on the class instance/object that the getter would then read. Or you could use a closure upon creating your object then your getter could access it from the outer scope.

As an instance/object property

var obj = {
    url:null,
    get href(){
       return this.url ? this.url.location.href : "";
    }
}

obj.url = {location:{href:"http://stackoverflow.com"}};
console.log( obj.href );

With an enclosure

function URIController(url){
    //You could also use `Object.defineProperty` to 
    //create the getter on a existing object
    return {
       get href(){
          return url.location.href;
       }
    }
}
var obj = URIController({location:{href:"http://stackoverflow.com"}});
console.log( obj.href );

rudi Ladeon · Accepted Answer · 2016-05-21 17:57:48Z

7

No, you can't pass an argument to a " getter " use a " setter " rather.

answered May 21, 2016 at 17:57

rudi Ladeon

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