You can use getters mutating an object for this task. But why do you need this?
On 24 Oct 2017 7:25 pm, "/#!/JoePea" <[email protected]> wrote: > Well, I know I can set accessors on a prototype easily, but what I > mean is, I need each instance of an `Element` to have exactly one > instance of something right after construction during the same > synchronous operation. > > For example, if we have an application with a bunch of pre-existing > Elements that do not extend from any classes of mine, I'd like for the > all to have `foo` properties, so that I can do this: > > ```js > const el = new SomeCustomElementThatWasDefinedCreatedByMe > console.log(el.foo) // it exists and is specific to the instance, not > a prototype property > > // or > > const div = document.createElement('div') > console.log(div.foo) // it exists and is specific to the instance, not > a prototype property > ``` > > Can this be done? > /#!/JoePea > > > On Tue, Oct 24, 2017 at 10:19 AM, /#!/JoePea <[email protected]> wrote: > >> This feels like a problem similar to https://esdiscuss.org/topic/ > block-scoped-prototype-extensions > > > > @Boris, even if it were scoped, how do we monkey patch a > > *constructor*? By the way, for some reason your link to > > `https://esdiscuss.org/topic/block-scoped-prototype-extensions` posted > > as `https://esdiscuss.org/topic/block` which is 404. If you can edit > > it it would help others not to stumble on a broken link. > > > >> if that would be possible, then everyone could just monkey patch > Object, right? > > > > But everyone can monkey patch the entire class already, aside from the > > constructor, by modifying the prototype. Obviously if someone returns > > something new from the constructor they might break everything, but it > > will be completely obvious and people then won't do that. The same > > applies with methods and properties, it is super easy to break entire > > applications monkey patching methods. > > > > --- > > > > So suppose I want to "polyfill" a concept. For example, I want all > > elements to have a new "foo" accessor after they've been constructed. > > Or for example, suppose `HTMLElement.prototype.style` and > > `SVGElement.prototype.style` didn't exist yet. How would I patch those > > in? > > /#!/JoePea > > > > > > On Tue, Oct 24, 2017 at 10:07 AM, Michał Wadas <[email protected]> > wrote: > >> AFAIR DOM classes are not extensible by any means. > >> > >> > >> > >> On 24 Oct 2017 6:51 pm, "/#!/JoePea" <[email protected]> wrote: > >>> > >>> Is it possible to monkey-patch an intermediate constructor of a > built-in > >>> subclass? > >>> > >>> For example, suppose I want all `Element` instances in a web app to > have > >>> new instance properties, is there a way to monkey-patch the Element > >>> constructor so that when I make a custom element by extending a > subclass of > >>> `Element` that the new logic will fire? > >>> > >>> For example: > >>> > >>> ```js > >>> // monkey-patch the Element constructor somehow so that it logs > "patched > >>> in Element". > >>> > >>> // then > >>> class FooBar extends HTMLElement {} > >>> customElement.define('foo-bar', FooBar) > >>> new FooBar // "patched in Element" > >>> ``` > >>> > >>> I tried > >>> > >>> ```js > >>> const OldElement = window.Element > >>> > >>> window.Element = function Element() { > >>> const _this = new OldElement > >>> console.log("patched in Element") > >>> return _this > >>> } > >>> > >>> window.Element.prototype = OldElement.prototype > >>> window.Element.prototype.constructor = window.Element > >>> > >>> class FooBar extends HTMLElement {} > >>> customElements.define('f-b', FooBar) > >>> new FooBar // does not log "patched in Element" > >>> ``` > >>> > >>> But when I make a new custom element, constructing it seems to use the > old > >>> Element constructor, as if a non-global reference to the original > >>> constructor is kept inside a module so that modifying the global > wouldn't > >>> have any effect. > >>> > >>> Is there a way to monkey patch a constructor in the middle of a > built-in > >>> prototype chain or to otherwise inject construction logic to base > classes of > >>> existing class hierarchies? > >>> > >>> > >>> /#!/JoePea > >>> > >>> _______________________________________________ > >>> es-discuss mailing list > >>> [email protected] > >>> https://mail.mozilla.org/listinfo/es-discuss > >>> > >> >
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