106 lines
3.2 KiB
Plaintext
106 lines
3.2 KiB
Plaintext
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---
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description: 'Enforce unbound methods are called with their expected scope.'
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---
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> 🛑 This file is source code, not the primary documentation location! 🛑
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>
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> See **https://typescript-eslint.io/rules/unbound-method** for documentation.
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Class method functions don't preserve the class scope when passed as standalone variables ("unbound").
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If your function does not access `this`, [you can annotate it with `this: void`](https://www.typescriptlang.org/docs/handbook/2/functions.html#declaring-this-in-a-function), or consider using an arrow function instead.
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Otherwise, passing class methods around as values can remove type safety by failing to capture `this`.
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This rule reports when a class method is referenced in an unbound manner.
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:::note Tip
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If you're working with `jest`, you can use [`eslint-plugin-jest`'s version of this rule](https://github.com/jest-community/eslint-plugin-jest/blob/main/docs/rules/unbound-method.md) to lint your test files, which knows when it's ok to pass an unbound method to `expect` calls.
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:::
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## Examples
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<!--tabs-->
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### ❌ Incorrect
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```ts
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class MyClass {
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public log(): void {
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console.log(this);
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}
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}
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const instance = new MyClass();
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// This logs the global scope (`window`/`global`), not the class instance
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const myLog = instance.log;
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myLog();
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// This log might later be called with an incorrect scope
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const { log } = instance;
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// arith.double may refer to `this` internally
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const arith = {
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double(x: number): number {
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return x * 2;
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},
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};
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const { double } = arith;
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```
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### ✅ Correct
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```ts
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class MyClass {
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public logUnbound(): void {
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console.log(this);
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}
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public logBound = () => console.log(this);
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}
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const instance = new MyClass();
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// logBound will always be bound with the correct scope
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const { logBound } = instance;
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logBound();
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// .bind and lambdas will also add a correct scope
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const dotBindLog = instance.logBound.bind(instance);
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const innerLog = () => instance.logBound();
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// arith.double explicitly declares that it does not refer to `this` internally
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const arith = {
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double(this: void, x: number): number {
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return x * 2;
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},
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};
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const { double } = arith;
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```
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## Options
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### `ignoreStatic`
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Examples of **correct** code for this rule with `{ ignoreStatic: true }`:
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```ts option='{ "ignoreStatic": true }' showPlaygroundButton
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class OtherClass {
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static log() {
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console.log(OtherClass);
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}
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}
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// With `ignoreStatic`, statics are assumed to not rely on a particular scope
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const { log } = OtherClass;
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log();
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```
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## When Not To Use It
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If your project dynamically changes `this` scopes around in a way TypeScript has difficulties modeling, this rule may not be viable to use.
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One likely difficult pattern is if your code intentionally waits to bind methods after use, such as by passing a `scope: this` along with the method.
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You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule.
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If you're wanting to use `toBeCalled` and similar matches in `jest` tests, you can disable this rule for your test files in favor of [`eslint-plugin-jest`'s version of this rule](https://github.com/jest-community/eslint-plugin-jest/blob/main/docs/rules/unbound-method.md).
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