description Optional

A string. A description of the symbol which can be used for debugging but not to access the symbol itself.

To create a new primitive symbol, you write Symbol() with an optional string as its description:

const sym1 = Symbol();
const sym2 = Symbol('foo');
const 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

The following syntax with the new operator will throw a TypeError:

const 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 Boolean, new String and new Number).

If you really want to create a Symbol wrapper object, you can use the Object() function:

const sym = Symbol('foo');
const symObj = Object(sym);
typeof sym    // => "symbol"
typeof symObj // => "object"

• Polyfill of Symbol in core-js