core-js/internals/symbol-define-to-primitive.js

'use strict';
var call = require('../internals/function-call');
var getBuiltIn = require('../internals/get-built-in');
var wellKnownSymbol = require('../internals/well-known-symbol');
var defineBuiltIn = require('../internals/define-built-in');

module.exports = function () {
  var Symbol = getBuiltIn('Symbol');
  var SymbolPrototype = Symbol && Symbol.prototype;
  var valueOf = SymbolPrototype && SymbolPrototype.valueOf;
  var TO_PRIMITIVE = wellKnownSymbol('toPrimitive');

  if (SymbolPrototype && !SymbolPrototype[TO_PRIMITIVE]) {
    // `Symbol.prototype[@@toPrimitive]` method
    // https://tc39.es/ecma262/#sec-symbol.prototype-@@toprimitive
    // eslint-disable-next-line no-unused-vars -- required for .length
    defineBuiltIn(SymbolPrototype, TO_PRIMITIVE, function (hint) {
      return call(valueOf, this);
    }, { arity: 1 });
  }
};