es.function.name.js

var DESCRIPTORS = require('../internals/descriptors');
var defineProperty = require('../internals/object-define-property').f;

var FunctionPrototype = Function.prototype;
var FunctionPrototypeToString = FunctionPrototype.toString;
var nameRE = /^\s*function ([^ (]*)/;
var NAME = 'name';

// Function instances `.name` property
// https://tc39.github.io/ecma262/#sec-function-instances-name
if (DESCRIPTORS && !(NAME in FunctionPrototype)) {
  defineProperty(FunctionPrototype, NAME, {
    configurable: true,
    get: function () {
      try {
        return FunctionPrototypeToString.call(this).match(nameRE)[1];
      } catch (error) {
        return '';
      }
    }
  });
}