JS.TS.NO.UNNECESSARY.TYPE.ASSERTION
Warns if a type assertion does not change the type of an expression
This rule prohibits using a type assertion that does not change the type of an expression.
Rule Details
This rule aims to prevent unnecessary type assertions.
Examples of code for this rule:
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Incorrect
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const foo = 3;
const bar = foo!;
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const foo = <3>3;
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type Foo = 3;
const foo = <Foo>3;
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type Foo = 3;
const foo = 3 as Foo;
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function foo(x: number): number {
return x!; // unnecessary non-null
}
Correct
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const foo = <number>3;
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const foo = 3 as number;
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const foo = 'foo' as const;
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function foo(x: number | undefined): number {
return x!;
}
Options
This rule optionally takes an object with a single property typesToIgnore, which can be set to a list of type names to ignore.
For example, with @typescript-eslint/no-unnecessary-type-assertion: ["error", { typesToIgnore: ['Foo'] }], the following is correct code":
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type Foo = 3;
const foo: Foo = 3;
When Not To Use It
If you don't care about having no-op type assertions in your code, then you can turn off this rule.