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Symbol : Object

primitive

Symbols are an alternate to using Strings as the keys for properties. Symbols allow hiding properties on Objects since you can only access the values if you have the same instance of the Symbol. You access a property with a Symbol key using object[symbol].

ECMAScript 2015 Spec

Symbol([description : String]) : Symbol

Creates a new Symbol with an optional description.

Example:

var myObject = { foo: 'bar' };

var mySymbol = Symbol('MySymbol');

myObject[mySymbol] = 'baz';

console.log(myObject[mySymbol]);

// The property cannot be accessed using a string
console.log(myObject['MySymbol']);

Results:

Instance Properties

description : String

Returns the description passed to the Symbol during construction.

Example:

var mySymbol = Symbol('MySymbol');
console.log(mySymbol.description);

Results:

ECMAScript 2019 Spec

Symbol Properties

asyncIterator : Symbol

hasInstance : Symbol

isConcatSpreadable : Symbol

iterator : Symbol

The Symbol that retrieves a function that returns an iterator for the Object.

Example:

// Array's iterator function is also exposed as 'values'
var arrayIterator = Array.prototype[Symbol.iterator];
console.log(arrayIterator === Array.prototype.values);

var x = ['a', 'b', 'c'];

// The following are all equivalent:
for (var item of x[Symbol.iterator]()) {
  console.log(item);
}

// for (... of ...) automatically invokes the iterator function
for (var item of x) { 
  console.log(item);
}

// Array[Symbol.iterator] is also available through Array.values
for (var item of x.values()) {
  console.log(item);
}

Results:

match : Symbol

matchAll : Symbol

replace : Symbol

search : Symbol

species : Symbol

split : Symbol

toPrimitive : Symbol

toStringTag : Symbol

unscopables : Symbol

Symbol Methods

for(key : String) : Symbol

keyFor(key : String) : Symbol

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