why declare method within square brackets wrapped around name in typescript?

Question

I've been going through nativescript code base to see how to update some of my plugins for {N} 3.0.1, and i see a lot of class methods this way.

[srcProperty.setNative](value: any) {
    this._createImageSourceFromSrc(value);
}

see the contents of image-common.ts and image.android.ts to see the full source.

why are the properties of the exported const from image-common.ts used in image.android.ts a methods, and why are they wrapped in square brackets ?

score 3 · Accepted Answer · answered Jul 01 '17 at 18:47

It generates a property with the computed name on that class's prototype.

While not very used this perfectly valid javascript/typescript code. It does result in some loss of typing though.

This typescript code:

let propName = 'someMethod';

class A {
  [propName](): number {
    console.log(propName);
    return 5;
  }
}

let a = new A();

let x = a[propName]()

Will result in this javascript output.

var propName = 'someMethod';
var A = (function () {
    function A() {
    }
    A.prototype[propName] = function () {
        console.log(propName);
        return 5;
    };
    return A;
}());
var a = new A();
var x = a[propName]();

You can see a working example here.

it is highly unusual, first time I see it too, but it makes sense. from a syntax point of view. — toskv, Jul 01 '17 at 22:27

why declare method within square brackets wrapped around name in typescript?

1 Answers1