javascript - 为什么可以打印 try 和 catch 对象，但任何普通对象都不能

Question

我是 JavaScript 的初学者，我正在研究 try 和 catch 错误处理技术，直到我注意到 catch 对象可以被打印，但任何普通对象都不能打印，

   try{
    throw new Error("Manually Thrown Exception");
    }
    catch(errHanlder){
    alert(errHanlder);  // it will give (ERROR:Manually Throw Exception)
    }

<小时/>

任何创建的对象都不是例如:

var obj={name:"User"};
alert(obj);   //it will give [object Object] 

为什么尽管它们的类型都是对象，但这种奇怪的行为是可能的

Answer 1

该对象拥有一个toString函数。

来自the MDN :

Every object has a toString() method that is automatically called when the object is to be represented as a text value or when an object is referred to in a manner in which a string is expected. By default, the toString() method is inherited by every object descended from Object. If this method is not overridden in a custom object, toString() returns "[object type]", where type is the object type.

对于错误，它是 this one .

它在 the ECMAScript standard 中定义:

您可以执行相同的操作，甚至无需在原型(prototype)级别进行定义:

 var obj = {name:"Albert", toString(){ return "User: " + this.name }};
 alert(obj);