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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
87 lines
2.5 KiB
Markdown
87 lines
2.5 KiB
Markdown
# Disallow unnecessary function binding (no-extra-bind)
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The `bind()` method is used to create functions with specific `this` values and, optionally, binds arguments to specific values. When used to specify the value of `this`, it's important that the function actually uses `this` in its function body. For example:
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```js
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var boundGetName = (function getName() {
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return this.name;
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}).bind({ name: "ESLint" });
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console.log(boundGetName()); // "ESLint"
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```
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This code is an example of a good use of `bind()` for setting the value of `this`.
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Sometimes during the course of code maintenance, the `this` value is removed from the function body. In that case, you can end up with a call to `bind()` that doesn't accomplish anything:
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```js
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// useless bind
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var boundGetName = (function getName() {
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return "ESLint";
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}).bind({ name: "ESLint" });
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console.log(boundGetName()); // "ESLint"
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```
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In this code, the reference to `this` has been removed but `bind()` is still used. In this case, the `bind()` is unnecessary overhead (and a performance hit) and can be safely removed.
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## Rule Details
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This rule is aimed at avoiding the unnecessary use of `bind()` and as such will warn whenever an immediately-invoked function expression (IIFE) is using `bind()` and doesn't have an appropriate `this` value. This rule won't flag usage of `bind()` that includes function argument binding.
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**Note:** Arrow functions can never have their `this` value set using `bind()`. This rule flags all uses of `bind()` with arrow functions as a problem
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Examples of **incorrect** code for this rule:
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```js
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/*eslint no-extra-bind: "error"*/
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/*eslint-env es6*/
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var x = function () {
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foo();
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}.bind(bar);
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var x = (() => {
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foo();
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}).bind(bar);
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var x = (() => {
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this.foo();
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}).bind(bar);
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var x = function () {
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(function () {
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this.foo();
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}());
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}.bind(bar);
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var x = function () {
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function foo() {
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this.bar();
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}
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}.bind(baz);
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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 no-extra-bind: "error"*/
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var x = function () {
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this.foo();
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}.bind(bar);
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var x = function (a) {
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return a + 1;
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}.bind(foo, bar);
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```
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## When Not To Use It
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If you are not concerned about unnecessary calls to `bind()`, you can safely disable this rule.
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## Further Reading
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* [Function.prototype.bind](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind)
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* [Understanding JavaScript's Function.prototype.bind](https://www.smashingmagazine.com/2014/01/understanding-javascript-function-prototype-bind/)
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