javascript - 为什么 Object.prototype.toString 返回 [object Object]

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我的代码如下所示

var obj = { name: 'John' }
var x = obj.toString();// produce "[object Object]"

alert(x)

我想知道为什么 Object.prototype.toString实现返回 [object Object]以及为什么没有实现返回 "{name: 'John'}" ?

Answer 1

根据ECMAScript Language Specification :

15.2.4.2 Object.prototype.toString ( ) When the toString method is called, the following steps are taken:

1. If the this value is undefined, return "[object Undefined]".
2. If the this value is null, return "[object Null]".
3. Let O be the result of calling ToObject passing the this value as the argument.
4. Let class be the value of the [[Class]] internal property of O.
5. Return the String value that is the result of concatenating the three Strings "[object ", class, and "]".

语言是这样设计的。我猜你得问 Brendan Eich 或 TC39。