Disallow unnecessary .call() and .apply(). (no-useless-call)

禁用不必要的 .call().apply()(no-useless-call)

The function invocation can be written by Function.prototype.call() and Function.prototype.apply(). But Function.prototype.call() and Function.prototype.apply() are slower than the normal function invocation.

函数的调用可以写成 Function.prototype.call()Function.prototype.apply(),但是 Function.prototype.call()Function.prototype.apply() 比正常的函数调用效率低。

Rule Details

This rule is aimed to flag usage of Function.prototype.call() and Function.prototype.apply() that can be replaced with the normal function invocation.

此规则的目的在于标记出可以被正常函数调用所替代的 Function.prototype.call()Function.prototype.apply() 的使用。

Examples of incorrect code for this rule:

错误 代码示例:

/*eslint no-useless-call: "error"*/

// These are same as `foo(1, 2, 3);`
foo.call(undefined, 1, 2, 3);
foo.apply(undefined, [1, 2, 3]);
foo.call(null, 1, 2, 3);
foo.apply(null, [1, 2, 3]);

// These are same as `obj.foo(1, 2, 3);`
obj.foo.call(obj, 1, 2, 3);
obj.foo.apply(obj, [1, 2, 3]);

Examples of correct code for this rule:

正确 代码示例:

/*eslint no-useless-call: "error"*/

// The `this` binding is different.
foo.call(obj, 1, 2, 3);
foo.apply(obj, [1, 2, 3]);
obj.foo.call(null, 1, 2, 3);
obj.foo.apply(null, [1, 2, 3]);
obj.foo.call(otherObj, 1, 2, 3);
obj.foo.apply(otherObj, [1, 2, 3]);

// The argument list is variadic.
foo.apply(undefined, args);
foo.apply(null, args);
obj.foo.apply(obj, args);

Known Limitations

This rule compares code statically to check whether or not thisArg is changed. So if the code about thisArg is a dynamic expression, this rule cannot judge correctly.

此规则通过静态地对比代码检测 thisArg 是否被改变。所以如果 thisArg 是个动态表达式,此规则不能作出正确的判断。

Examples of incorrect code for this rule:

错误 代码示例:

/*eslint no-useless-call: "error"*/

a[i++].foo.call(a[i++], 1, 2, 3);

Examples of correct code for this rule:

正确 代码示例:

/*eslint no-useless-call: "error"*/

a[++i].foo.call(a[i], 1, 2, 3);

When Not To Use It

If you don’t want to be notified about unnecessary .call() and .apply(), you can safely disable this rule.

如果你不想收到关于不必要的 .call().apply()的通知,你可以禁用此规则。

Version

This rule was introduced in ESLint 1.0.0-rc-1.

该规则在 ESLint 1.0.0-rc-1 中被引入。

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