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docs: [no-unsafe-call] clarify that you can never safely narrow Function #10058

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Merged
merged 3 commits into from
Oct 10, 2024
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docs: [no-unsafe-call] clarify that you can never safely narrow Function #10058

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docs: [no-unsafe-call] clarify that you can never safely narrow function
kirkwaiblinger Sep 25, 2024
2a0cbf5
more to the point
kirkwaiblinger Sep 29, 2024
d1bb0bd
Merge branch 'main' into unsafe-function-call
kirkwaiblinger Sep 29, 2024
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19 changes: 18 additions & 1 deletion packages/eslint-plugin/docs/rules/no-unsafe-call.mdx
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Expand Up @@ -78,7 +78,7 @@ Note that whereas [no-unsafe-function-type](./no-unsafe-function-type.mdx) helps
See, for example, the following code:

```ts
function unsafe(maybeFunction: unknown): string {
function callUnsafe(maybeFunction: unknown): string {
if (typeof maybeFunction === 'function') {
// TypeScript allows this, but it's completely unsound.
return maybeFunction('call', 'with', 'any', 'args');
Expand All @@ -87,6 +87,23 @@ function unsafe(maybeFunction: unknown): string {
}
```

In this sort of situation, beware that there is no way to guarantee with runtime checks that a value is safe to call.
If you _really_ want to call a value whose type you don't know, your best best is to use a `try`/`catch` and suppress any TypeScript or linter errors that get in your way.

```ts
function callSafe(maybeFunction: unknown): void {
try {
// intentionally unsound type assertion
(maybeFunction as () => unknown)();
} catch (e) {
console.error(
'Function either could not be called or threw an error when called: ',
e,
);
}
}
```

## When Not To Use It

If your codebase has many existing `any`s or areas of unsafe code, it may be difficult to enable this rule.
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