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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
125 lines
2.9 KiB
Markdown
125 lines
2.9 KiB
Markdown
# Enforce that class methods utilize `this` (class-methods-use-this)
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If a class method does not use `this`, it can *sometimes* be made into a static function. If you do convert the method into a static function, instances of the class that call that particular method have to be converted to a static call as well (`MyClass.callStaticMethod()`)
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It's possible to have a class method which doesn't use `this`, such as:
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```js
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class A {
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constructor() {
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this.a = "hi";
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}
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print() {
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console.log(this.a);
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}
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sayHi() {
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console.log("hi");
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}
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}
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let a = new A();
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a.sayHi(); // => "hi"
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```
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In the example above, the `sayHi` method doesn't use `this`, so we can make it a static method:
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```js
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class A {
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constructor() {
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this.a = "hi";
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}
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print() {
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console.log(this.a);
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}
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static sayHi() {
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console.log("hi");
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}
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}
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A.sayHi(); // => "hi"
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```
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Also note in the above examples that if you switch a method to a static method, *instances* of the class that call the static method (`let a = new A(); a.sayHi();`) have to be updated to being a static call (`A.sayHi();`) instead of having the instance of the *class* call the method
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## Rule Details
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This rule is aimed to flag class methods that do not use `this`.
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Examples of **incorrect** code for this rule:
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```js
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/*eslint class-methods-use-this: "error"*/
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/*eslint-env es6*/
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class A {
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foo() {
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console.log("Hello World"); /*error Expected 'this' to be used by class method 'foo'.*/
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}
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}
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```
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Examples of **correct** code for this rule:
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```js
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/*eslint class-methods-use-this: "error"*/
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/*eslint-env es6*/
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class A {
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foo() {
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this.bar = "Hello World"; // OK, this is used
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}
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}
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class A {
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constructor() {
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// OK. constructor is exempt
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}
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}
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class A {
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static foo() {
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// OK. static methods aren't expected to use this.
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}
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}
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```
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## Options
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### Exceptions
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```
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"class-methods-use-this": [<enabled>, { "exceptMethods": [<...exceptions>] }]
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```
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The `exceptMethods` option allows you to pass an array of method names for which you would like to ignore warnings. For example, you might have a spec from an external library that requires you to overwrite a method as a regular function (and not as a static method) and does not use `this` inside the function body. In this case, you can add that method to ignore in the warnings.
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Examples of **incorrect** code for this rule when used without exceptMethods:
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```js
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/*eslint class-methods-use-this: "error"*/
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class A {
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foo() {
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}
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}
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```
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Examples of **correct** code for this rule when used with exceptMethods:
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```js
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/*eslint class-methods-use-this: ["error", { "exceptMethods": ["foo"] }] */
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class A {
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foo() {
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}
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}
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```
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## Further Reading
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* [Classes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes)
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* [Static Methods](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static)
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