custom input validator function example contains syntax error and is unclear

[michahell]

the following example, here:
https://material.angular.io/components/input/overview
located under Custom Error Matcher contains one too many right brackets
and on top of that, is unclear:

function myErrorStateMatcher(control: FormControl, form: FormGroupDirective | NgForm): boolean {
  // Error when invalid control is dirty, touched, or submitted
  const isSubmitted = form && form.submitted;
  return !!(control.invalid && (control.dirty || control.touched || isSubmitted)));
}

why not just use:

return control.invalid && (control.dirty || control.touched || isSubmitted);

?

[willshowell]

Good catch on the extra right parentheses.

For the boolean coercion, that example was based on the existing default matcher. It originates from #3560 (comment)

[michahell]

ty, but why is coercion necessary? does && not already do that ? or is there some javascript wat involved if any of the control.dirty or other properties are not booleans? if so, wat.

[willshowell]

Yeah I think in this case it is not actually necessary (maybe just for safety?). && uses the last value, but as long as dirty, touched, and submitted are all boolean, there should be no need to coerce it.

> 1 && true
true

> true && 1
1

> !!(true && 1)
true

[michahell]

A case of wat, it was, then :) I unconsciously knew this about &&, but only now realise that coercing might sometimes be necessary, thanks!

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