Disallow unnecessary function binding (no-extra-bind)

禁止不必要的函数绑定 (no-extra-bind)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

命令行中的 --fix 选项可以自动修复一些该规则报告的问题。

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:

bind() 方法使用特定的 this 值来创建函数，并可选地将参数绑定到特定的值。当使用 this 时，在函数体中实际上使用的 this 值。例如：

var boundGetName = (function getName() {
    return this.name;
}).bind({ name: "ESLint" });

console.log(boundGetName());      // "ESLint"

This code is an example of a good use of bind() for setting the value of this.

这段代码就是一个很好的例子，它使用 bind() 来设置 this 值。

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:

有时，在代码维护过程中，bind() 不再传入 this。在这种情况下，你可以不调用 bind()，因为它没有做任何事情。

// useless bind
var boundGetName = (function getName() {
    return "ESLint";
}).bind({ name: "ESLint" });

console.log(boundGetName());      // "ESLint"

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.

在这段代码中，this 的引用已经被删除，但是 bind() 仍在使用。在这种情况下，bind() 就成了不必要的开销（和性能损耗），可以安全地删除。

Rule Details

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.

此规则目的在于避免不必要的 bind() 使用，并且当立即执行的函数表达式 (IIFE) 使用 bind()，但是没有一个合适的 this 值时，该规则会发出警告。此规则不会标记有函数参数绑定的bind() 的使用情况。

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

注意：箭头函数不能通过使用 bind() 设置它们的自己 this 值。此规则把所有使用bind() 的箭头函数标记为是有问题的。

Examples of incorrect code for this rule:

错误 代码示例：

/*eslint no-extra-bind: "error"*/
/*eslint-env es6*/

var x = function () {
    foo();
}.bind(bar);

var x = (() => {
    foo();
}).bind(bar);

var x = (() => {
    this.foo();
}).bind(bar);

var x = function () {
    (function () {
      this.foo();
    }());
}.bind(bar);

var x = function () {
    function foo() {
      this.bar();
    }
}.bind(baz);

Examples of correct code for this rule:

正确 代码示例：

/*eslint no-extra-bind: "error"*/

var x = function () {
    this.foo();
}.bind(bar);

var x = function (a) {
    return a + 1;
}.bind(foo, bar);

When Not To Use It

If you are not concerned about unnecessary calls to bind(), you can safely disable this rule.

如果你不担心不必要的 bind() 调用，你可以禁用此规则。

Further Reading

Version

This rule was introduced in ESLint 0.8.0.

该规则在 ESLint 0.8.0 中被引入。

Resources