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.
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.
The well-known symbol @@toStringTag
.
Property attributes of Symbol.toStringTag
| |
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
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
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.
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
When creating your own class, JavaScript defaults to the "Object" tag:
class ValidatorClass {} Object.prototype.toString.call(new ValidatorClass()); // "[object Object]"
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]"
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"
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
toStringTag |
49 | 15 | 51 | 36 | 10 | 49 | 51 | 36 | 10 | 5.0 | 49 | 1.0 | 6.0.0 | |
dom_objects |
50 | 79 | 78 | 37 | 14 | 50 | 79 | 37 | 14 | 5.0 | 50 | 1.0 | No |
© 2005–2023 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/toStringTag