Feature Request / Proposal: constructor type guard

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');
}

related to #3841

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.

i’d like to work on this 😄

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

Hey. Why was this closed? :(

Because #32774 is merged.

Nathan Shively-Sanders (@sandersn)

The snippet in the issue doesn't work. Nathan Shively-Sanders (@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');
}

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Feature Request / Proposal: constructor type guard #23274

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Feature Request / Proposal: constructor type guard #23274

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mhegazy commented on Apr 10, 2018

RyanCavanaugh commented on Apr 17, 2018

Kingwl commented on Apr 22, 2018

austincummings commented on Jul 2, 2019

bruce-forte commented on May 21, 2020

Kingwl commented on May 21, 2020

ikonst commented on Jun 24, 2024

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