X.prototype.y called on incompatible type

错误提示

TypeError: Function.prototype.toString called on incompatible object (Firefox)
TypeError: Function.prototype.bind called on incompatible target (Firefox)
TypeError: Method Set.prototype.add called on incompatible receiver undefined (Chrome)
TypeError: Bind must be called on a function (Chrome)

错误类型

TypeError

哪里出错了?

当这个错误被抛出时,属于某个对象的函数被调用,但是没有提供给 this 与其所期望的函数类型一致的参数。

在调用 Function.prototype.call()Function.prototype.apply() 方法,但是为 this 提供的绑定对象与预期的不匹配时,这个问题就会出现。

该问题还会出现于将一个(存储在一个对象中的)函数提供给另外一个函数作为参数时。在这种情况下,函数所在的对象并非该函数的 this  绑定的目标对象。为了解决这个问题,你或者为其提供一个 lambda 表达式,该表达式完成函数要完成的任务,或者调用 Function.prototype.bind() 函数为 this 强制绑定期望的对象。

示例

错误示例

var mySet = new Set;
['bar', 'baz'].forEach(mySet.add);
// mySet.add is a function, but "mySet" is not captured as this.

var myFun = function () {};
['bar', 'baz'].forEach(myFun.bind);
// myFun.bind is a function, but "myFun" is not captured as this.

正确示例

var mySet = new Set;
['bar', 'baz'].forEach(mySet.add.bind(mySet));
// This works due to binding "mySet" as this.

var myFun = function () {};
['bar', 'baz'].forEach(x => myFun.bind(x));
// This works using the "bind" function. It creates a lambda forwarding the argument.

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