Widely availableSupported across all major browsers. Safe to use in production.
Primitive types Widely available

Symbol

A Symbol value is a unique, non-enumerable primitive value used for encapsulation or information hiding. For example, a symbol can be a key of an object that can never collide with any other key.

Primitive types

Overview

A Symbol value is a unique, non-enumerable primitive value used for encapsulation or information hiding. For example, a symbol can be a key of an object that can never collide with any other key.

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
Symbol
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Array.@@species

The Array[Symbol.species] static accessor property returns the constructor used to construct return values from array methods.
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Symbol.@@toPrimitive

The [Symbol.toPrimitive]() method of Symbol values returns this symbol value.
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Symbol.Symbol

The Symbol() function returns primitive values of type Symbol.
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Symbol.description

The description accessor property of Symbol values returns a string containing the description of this symbol, or undefined if the symbol has no description.
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Symbol.for

The Symbol.for() static method searches for existing symbols in a runtime-wide symbol registry with the given key and returns it if found. Otherwise a new symbol gets created in the global symbol registry with this key.
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Symbol.hasInstance

The Symbol.hasInstance static data property represents the well-known symbol Symbol.hasInstance. The Operators/instanceof operator looks up this symbol on its right-hand operand for the method used to determine if the constructor object recognizes an object as its instance.
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Symbol.isConcatSpreadable

The Symbol.isConcatSpreadable static data property represents the well-known symbol Symbol.isConcatSpreadable. The Array.prototype.concat() method looks up this symbol on each object being concatenated to determine if it should be treated as an array-like object and flattened to its array elements.
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Symbol.iterator

The Symbol.iterator static data property represents the well-known symbol Symbol.iterator. The iterable protocol looks up this symbol for the method that returns the iterator for an object. In order for an object to be iterable, it must have a [Symbol.iterator] key.
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Symbol.keyFor

The Symbol.keyFor() static method retrieves a shared symbol key from the global symbol registry for the given symbol.
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Symbol.match

The Symbol.match static data property represents the well-known symbol Symbol.match. The String.prototype.match() method looks up this symbol on its first argument for the method used to match an input string against the current object. This symbol is also used to determine if an object should be treated as a regex.
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Symbol.matchAll

The Symbol.matchAll static data property represents the well-known symbol Symbol.matchAll. The String.prototype.matchAll() method looks up this symbol on its first argument for the method that returns an iterator, that yields matches of the current object against a string.
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Symbol.replace

The Symbol.replace static data property represents the well-known symbol Symbol.replace. The String.prototype.replace() and String.prototype.replaceAll() methods look up this symbol on their first argument for the method that replaces substrings matched by the current object.
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Symbol.search

The Symbol.search static data property represents the well-known symbol Symbol.search. The String.prototype.search() method looks up this symbol on its first argument for the method that returns the index within a string that matches the current object.
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Symbol.species

The Symbol.species static data property represents the well-known symbol Symbol.species. Methods that create copies of an object may look up this symbol on the object for the constructor function to use when creating the copy.
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Symbol.split

The Symbol.split static data property represents the well-known symbol Symbol.split. The String.prototype.split() method looks up this symbol on its first argument for the method that splits a string at the indices that match the current object.
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Symbol.toPrimitive

The Symbol.toPrimitive static data property represents the well-known symbol Symbol.toPrimitive. All type coercion algorithms look up this symbol on objects for the method that accepts a preferred type and returns a primitive representation of the object, before falling back to using the object's valueOf() and toString() methods.
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Symbol.toString

The toString() method of Symbol values returns a string representing this symbol value.
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Symbol.toStringTag

The Symbol.toStringTag static data property represents the well-known symbol 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.
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Symbol.toStringTag.dom objects

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:
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Symbol.valueOf

The valueOf() method of Symbol values returns this symbol value.
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1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)
Notes 1 item(s)
Implementation note
  • Edge 12 included Symbol properties in `JSON.stringify()` output.
Notes 3 item(s)
Limitation
  • This browser only partially implements this feature
Removed
  • This feature was removed in a later browser version (12.1)
Implementation note
  • No support for an undefined description.
Notes 3 item(s)
Limitation
  • This browser only partially implements this feature
Removed
  • This feature was removed in a later browser version (12.2)
Implementation note
  • No support for an undefined description.

Syntax

JAVASCRIPT 
const id = Symbol('id');
const user = { [id]: 123, name: 'Taro' };

user[id]; // 123
Object.keys(user); // ['name'] (Symbols are not enumerated)

// Well-known Symbol
class Range {
  constructor(start, end) { this.start = start; this.end = end; }
  [Symbol.iterator]() {
    let current = this.start;
    return { next: () => ({ value: current, done: current++ > this.end }) };
  }
}

Live demo

Symbol one

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PreviewFullscreen

privateproperty. simulate

Symbol ki- to and, Object.keys etc. Normal. columnraise from is hide..

PreviewFullscreen

Iterateprocessing. kastamize

Looppossible to.. with Symbol.iterator implementation,. Object for...of.

PreviewFullscreen

Use cases

  • Using Symbol

    A Symbol value is a unique, non-enumerable primitive value used for encapsulation or information hiding. For example, a symbol can be a key of an object that can never collide with any other key.

Cautions

  • No specific concerns. Stable across all major browsers.

Accessibility

  • When updating the DOM dynamically, announce important changes to assistive technology with aria-live regions.

Related links

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