Symbol.toStringTag

The Symbol.toStringTag well-known symbol is a string valued property that is used in the creation of the default string description of an object. It is accessed internally by the Object.prototype.toString() method.

Property attributes of Symbol.toStringTag
Writable no
Enumerable no
Configurable no

Description

Many JavaScript types have tags by default:

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

Others have a built-in toStringTag symbol defined:

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]"

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Symbol.toStringTag' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Symbol.toStringTag' in that specification.
Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 49 51 (51) No support ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? 51.0 (51) No support ? ?

See also

Document Tags and Contributors

 Contributors to this page: ZeikJT, fscholz
 Last updated by: ZeikJT,