lodash/isSymbol.js

define(['./isObjectLike'], function(isObjectLike) {

  /** `Object#toString` result references. */
  var symbolTag = '[object Symbol]';

  /** Used for built-in method references. */
  var objectProto = Object.prototype;

  /**
   * Used to resolve the
   * [`toStringTag`](http://ecma-international.org/ecma-262/6.0/#sec-object.prototype.tostring)
   * of values.
   */
  var objectToString = objectProto.toString;

  /**
   * Checks if `value` is classified as a `Symbol` primitive or object.
   *
   * @static
   * @memberOf _
   * @since 4.0.0
   * @category Lang
   * @param {*} value The value to check.
   * @returns {boolean} Returns `true` if `value` is correctly classified,
   *  else `false`.
   * @example
   *
   * _.isSymbol(Symbol.iterator);
   * // => true
   *
   * _.isSymbol('abc');
   * // => false
   */
  function isSymbol(value) {
    return typeof value == 'symbol' ||
      (isObjectLike(value) && objectToString.call(value) == symbolTag);
  }

  return isSymbol;
});