"no-unnecessary-type-assertion" flags necessary assertion Element as HTMLElement

[aaronbeall]

Bug Report

• TSLint version: ^5.8.0
• TypeScript version: ^2.6.2
• Running TSLint via: Package script: tslint --format stylish --project tsconfig.json

TypeScript code being linted

(ReactDOM.findDOMNode(this.toggle) as HTMLElement).focus()

with tslint.json configuration:

{
"no-unnecessary-type-assertion": true
}

Actual behavior

no-unnecessary-type-assertion This assertion is unnecessary since it does not change the type of the expression.

Expected behavior

No error. findDOMNode() returns Element which has no focus() method, subclass HTMLElement does so assertion is necessary.

The findDOMNode() definition from @types/react-dom looks like this:

declare namespace ReactDOM {
    function findDOMNode<E extends Element>(instance: ReactInstance): E;
}

Element comes from lib.es6.d.ts.

[ajafff]

This is a duplicate of #3540
The cause and the workaround are the same for this issue.

[aaronbeall]

@ajafff Thanks for the fast response! That thread explains it all and the workaround worked nicely in my case.