Symbol() constructor returns a value of type symbol, but is incomplete as a constructor because it does not support the syntax "
new Symbol()" and it is not intended to be subclassed. It may be used as the value of an
extends clause of a
class definition but a
super call to it will cause an exception.
To create a new primitive symbol, you write
Symbol() with an optional string as its description:
let sym1 = Symbol() let sym2 = Symbol('foo') let sym3 = Symbol('foo')
The above code creates three new symbols. Note that
Symbol("foo") does not coerce the string
"foo" into a symbol. It creates a new symbol each time:
Symbol('foo') === Symbol('foo') // false
let sym = new Symbol() // TypeError
This prevents authors from creating an explicit
Symbol wrapper object instead of a new symbol value and might be surprising as creating explicit wrapper objects around primitive data types is generally possible (for example,
new String and
If you really want to create a
Symbol wrapper object, you can use the
let sym = Symbol('foo'); let symObj = Object(sym); typeof sym // => "symbol" typeof symObj // => "object"
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