Mat autocomplete input change event bleeds 'event' object

[KissBalazs]

🐞 bug report

Affected Package

The issue is caused by package @angular/material 9.1.2

Is this a regression?

not sure.

Description

The event (change) will pass down an "event" object to the handler, even if it's not specified as a parameter.

🔬 Minimal Reproduction

https://stackblitz.com/edit/angular-x78zg6

see the autocomplete-overview-example.html lines 6-7, and their correspoding hander on autocomplete-verview-example.ts lines 65-72.

🔥 Exception or Error

console.log shows that we have an "event" object, although it is not defined in the function parameter list.

🌍 Your Environment

Angular Version:
see stackblitz dependencies.

[pkozlowski-opensource]

After a quick scan it looks like a duplicate of #4059 where we've got a conflict between the (change) event on an <input> and the change event raised by a directive. Needs more investigation.

[KissBalazs]

Might be connected to this issue, a button click handler also does the same thing:

<button (click)=handle()>...</button>

Also bleeds an "event" variable in handler:

public handle(){
   console.log(event); // this should not exist here, but does.
}

See this Stackblitz example.

[pkozlowski-opensource]

@KissBalazs I'm sorry but it is not clear from your stackblitz what is the issue that you are trying to illustrate... Is it about "most of the time" this exists here."??? If you are unsure if your issue is different from the one discussed here, please open a new issue but follow the issue template when doing so (most importantly we need a reproduce scenario that shows broken / non-working scenario).

[KissBalazs]

@pkozlowski-opensource sorry for the confusion, I have cleared up my comment.

[pkozlowski-opensource]

@KissBalazs thnx for the additional clarifications! You are totally right to be confused as to why one can access event! It turns out, though, that it is not Angular specific but you are bumping into https://developer.mozilla.org/en-US/docs/Web/API/Window/event

The long story short that browsers will expose event (for the event being processed) on the window. Since window acts as a global in the browser environment, you can access it in your event handler. You would observe the same effect Angular or not.

Going to close this one as it is not specific to Angular but rather to how browsers work. But hey, totally see how this could be confusing!

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