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  • Callable class instances

Callable class instances

# Michał Wadas (9 years ago)

Are there any plans/proposals to specify user defined callable objects?

It's possible to extend Function, but it requires to specify function code as string and prevents usage of local variables.

Eg:

class Foo {
    constructor() {
        this.i=0;
    }
    [Symbol.call]() {
        return class.instance.i++; // new meta property
    }
}
const f = new Foo;
typeof f === 'function';
f instanceof Function === false; // most use cases would be Function
instances
f() === 0;
f() === 1;
f.call(null); // TypeError: undefined is not a function
# Raul-Sebastian Mihăilă (9 years ago)

It seems to me that you are mixing Foo and f. If that's not intended then what you want can be obtained with:

var x = 0;

function Foo() {
if (new.target) {
this.i = 0;
} else {
// I don't know what class.instance is supposed to mean.
return x++;
}
}

Object.setPrototypeOf(Foo, null);

All the functions that we create are user defined callable objects.

# Raul-Sebastian Mihăilă (9 years ago)

Forgot about instanceof.

var x = 0;

function Foo() {
    if (new.target) {
        this.i = 0;
    } else {
        // I don't know what class.instance is supposed to mean.
        return x++;
    }
}

Object.setPrototypeOf(Foo, null);
Foo[Symbol.hasInstance] = () => false;
# Claude Pache (9 years ago)

Le 3 mars 2016 à 18:04, Michał Wadas <michalwadas at gmail.com> a écrit :

Are there any plans/proposals to specify user defined callable objects?

It's possible to extend Function, but it requires to specify function code as string and prevents usage of local variables.

Eg:

class Foo {
    constructor() {
        this.i=0;
    }
    [Symbol.call]() {
        return class.instance.i++; // new meta property 
    } 
} 
const f = new Foo;
typeof f === 'function';
f instanceof Function === false; // most use cases would be Function instances 
f() === 0;
f() === 1;
f.call(null); // TypeError: undefined is not a function

The following code should work (it did for me in Chrome):

class Foo {
    constructor() {
        let obj = () => obj.i++;
        Object.setPrototypeOf(obj, new.target.prototype);
        obj.i = 0;
        return obj;
    }
}