Add support for ES6 symbol types

[Gozala]

Code along this lines causes an error:

Class List {
  $$typeof: symbol;
  constructor() {
     this.$$typeof = Symbol.for('mylib/symbol')
  }
}

[Gozala]

I did not quite figured out how to add a primitive type support and at this point I don't have enough time to digg into to do it. So I have created this libdef for my use:

// See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol
declare class Symbol {
  static (value?:any): symbol;
  static for(key:string): symbol;
  static keyFor(symbol:symbol): string;
  toString(): string;
  valueOf(): symbol;
  // Well-known symbols
  static iterator: symbol;
  static match: symbol;
  static replace: symbol;
  static search: symbol;
  static split: symbol;
  static hasInstance: symbol;
  static isConcatSpreadable: symbol;
  static unscopables: symbol;
  static species: symbol;
  static toPrimitive: symbol;
  static toStringTag: symbol;
}

type symbol = Symbol;

I'm happy to send a pull to include it into core.js until proper support is built.

[eranimo]

Has Symbol.iterator support been implemented?

[kvanbere]

This would be really good to have because it is a common use-case with React Redux to use symbols for action namespacing (and slightly better performance, too).

Our current codebase massively fouls with flow and we've got a lot of $FlowFixMes caused by lack of Symbol support and support for symbols as map keys. ie

export const SOME_FOO = Symbol('SOME_FOO');

// ...
import { SOME_FOO } from './some/action/type';

export const {
    SOME_FOO: doSomeFoo,
    // ^ flow error, symbol not supported / can't use as map key
    ...
}

[kevinSuttle]

https://github.com/facebook/flow/blob/master/lib/core.js#L84 ?

[gajus]

Is there any plan to support Symbols?

https://flow.org/try/#0MYewdgzgLgBAYiEBlAngWwEYgDYwLwyqY4AUA5HAPKVkCUA3AFCiSwBCAhgE5Fa4G9SZNgEEASnSaMoKAA4BTGJwBeAFTmKCAbwA+jAJABqGQoBcME-JAAzeIkHYANIxiuYhgG4dsAV3kBGc2guAEswAHNGHQBfGB0YXQNjDXNLGyVuB2c3dy9feQAmczAfTHkuKOipFmgYDG58GBJ65XMVdQVafAA+BKrGRnquEi0DS3MEZHQ+bJh9PL8imH9GaIYgA

Currently typeof construct is useless for differentiating object shape, and symbol cannot be used as a literal value.

[SamChou19815]

Symbols support to be supported