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
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()
或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
js
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
js
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.