Symbol.toStringTag
Symbol.toStringTag
静态数据属性代表 众所周知的符号 @@toStringTag
。Object.prototype.toString()
在 this
值上查找此符号,以查找包含表示对象类型的字符串的属性。
¥The Symbol.toStringTag
static data property represents the well-known symbol @@toStringTag
. Object.prototype.toString()
looks up this symbol on the this
value for the property containing a string that represents the type of the object.
Try it
值
示例
默认标签
¥Default tags
有些值没有 Symbol.toStringTag
,但有特殊的 toString()
表示。完整列表请参见 Object.prototype.toString()
。
¥Some values do not have Symbol.toStringTag
, but have special toString()
representations. For a complete list, see Object.prototype.toString()
.
Object.prototype.toString.call("foo"); // "[object String]"
Object.prototype.toString.call([1, 2]); // "[object Array]"
Object.prototype.toString.call(3); // "[object Number]"
Object.prototype.toString.call(true); // "[object Boolean]"
Object.prototype.toString.call(undefined); // "[object Undefined]"
Object.prototype.toString.call(null); // "[object Null]"
// ... and more
内置 toStringTag 符号
¥Built-in toStringTag symbols
大多数内置对象都提供自己的 @@toStringTag
属性。几乎所有内置对象的 @@toStringTag
属性都是不可写、不可枚举、可配置的;Iterator
是个例外,出于兼容性原因,它是可写的。
¥Most built-in objects provide their own @@toStringTag
property. Almost all built-in objects' @@toStringTag
property is not writable, not enumerable, and configurable; the exception is Iterator
, which is writable for compatibility reasons.
对于像 Promise
这样的构造函数对象,该属性安装在 Constructor.prototype
上,这样构造函数的所有实例都继承 @@toStringTag
并且可以字符串化。对于像 Math
和 JSON
这样的非构造函数对象,该属性被安装为静态属性,以便命名空间对象本身可以被字符串化。有时,构造函数还提供自己的 toString
方法(例如 Intl.Locale
),在这种情况下,仅当你显式调用 Object.prototype.toString
时才使用 @@toStringTag
属性。
¥For constructor objects like Promise
, the property is installed on Constructor.prototype
, so that all instances of the constructor inherit @@toStringTag
and can be stringified. For non-constructor objects like Math
and JSON
, the property is installed as a static property, so that the namespace object itself can be stringified. Sometimes, the constructor also provides its own toString
method (for example, Intl.Locale
), in which case the @@toStringTag
property is only used when you explicitly call Object.prototype.toString
on it.
Object.prototype.toString.call(new Map()); // "[object Map]"
Object.prototype.toString.call(function* () {}); // "[object GeneratorFunction]"
Object.prototype.toString.call(Promise.resolve()); // "[object Promise]"
// ... and more
使用 toStringTag 自定义标签
¥Custom tag with toStringTag
创建自己的类时,JavaScript 默认使用 "对象" 标签:
¥When creating your own class, JavaScript defaults to the "Object" tag:
class ValidatorClass {}
Object.prototype.toString.call(new ValidatorClass()); // "[object Object]"
现在,在 toStringTag
的帮助下,你可以设置自己的自定义标签:
¥Now, with the help of toStringTag
, you are able to set your own custom tag:
class ValidatorClass {
get [Symbol.toStringTag]() {
return "Validator";
}
}
Object.prototype.toString.call(new ValidatorClass()); // "[object Validator]"
toStringTag 可用于所有 DOM 原型对象
¥toStringTag available on all DOM prototype objects
由于 2020 年中期的 WebIDL 规范变更,浏览器正在向所有 DOM 原型对象添加 Symbol.toStringTag
属性。例如,要访问 HTMLButtonElement
上的 Symbol.toStringTag
属性:
¥Due to a WebIDL spec change in mid-2020, browsers are adding a Symbol.toStringTag
property to all DOM prototype objects. For example, to access the Symbol.toStringTag
property on HTMLButtonElement
:
const test = document.createElement("button");
test.toString(); // "[object HTMLButtonElement]"
test[Symbol.toStringTag]; // "HTMLButtonElement"
规范
Specification |
---|
ECMAScript Language Specification # sec-symbol.tostringtag |
浏览器兼容性
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