Feature Request / Proposal: constructor type guard

[sheley1998]

In most cases, constructor comparison is faster than instanceof and typeof, thus using it as type guard can improve performance. The code below demonstrates the desired behavior:

const el:HTMLElement = document.createElement('canvas');

if (el.constructor === HTMLCanvasElement) {
    //inside of this scope, el is parsed as an instance of HTMLCanvasElement
    el.getContext('2d');
}

[mhegazy]

related to #3841

[RyanCavanaugh]

Accepting PRs for a new kind of type guard (IOW one that specifically looks for this syntactic pattern). Note that the false arm here can't perform any narrowing of a union due to constructor checks not identifying subclasses.

[Kingwl]

i’d like to work on this 😄

[austincummings]

Is this issue being worked? If not I'd like to try and add this.

[adam-arold]

Hey. Why was this closed? :(

[Kingwl]

Because #32774 is merged.

[ikonst]

The snippet in the issue doesn't work. @sandersn, can we reopen?

The only thing that works with #32774 is

const el: HTMLDivElement | HTMLCanvasElement = document.createElement(tagName);
if (el.constructor === HTMLCanvasElement) {
  //inside of this scope, el is parsed as an instance of HTMLCanvasElement
  el.getContext('2d');
}