core-js/modules/es.reflect.construct.js

'use strict';
var $ = require('../internals/export');
var getBuiltIn = require('../internals/get-built-in');
var apply = require('../internals/function-apply');
var bind = require('../internals/function-bind');
var aConstructor = require('../internals/a-constructor');
var anObject = require('../internals/an-object');
var isObject = require('../internals/is-object');
var create = require('../internals/object-create');
var fails = require('../internals/fails');

var nativeConstruct = getBuiltIn('Reflect', 'construct');
var ObjectPrototype = Object.prototype;
var push = [].push;

// `Reflect.construct` method
// https://tc39.es/ecma262/#sec-reflect.construct
// MS Edge supports only 2 arguments and argumentsList argument is optional
// FF Nightly sets third argument as `new.target`, but does not create `this` from it
var NEW_TARGET_BUG = fails(function () {
  function F() { /* empty */ }
  return !(nativeConstruct(function () { /* empty */ }, [], F) instanceof F);
});

var ARGS_BUG = !fails(function () {
  nativeConstruct(function () { /* empty */ });
});

var FORCED = NEW_TARGET_BUG || ARGS_BUG;

$({ target: 'Reflect', stat: true, forced: FORCED, sham: FORCED }, {
  construct: function construct(Target, args /* , newTarget */) {
    aConstructor(Target);
    anObject(args);
    var newTarget = arguments.length < 3 ? Target : aConstructor(arguments[2]);
    if (ARGS_BUG && !NEW_TARGET_BUG) return nativeConstruct(Target, args, newTarget);
    if (Target === newTarget) {
      // w/o altered newTarget, optimization for 0-4 arguments
      switch (args.length) {
        case 0: return new Target();
        case 1: return new Target(args[0]);
        case 2: return new Target(args[0], args[1]);
        case 3: return new Target(args[0], args[1], args[2]);
        case 4: return new Target(args[0], args[1], args[2], args[3]);
      }
      // w/o altered newTarget, lot of arguments case
      var $args = [null];
      apply(push, $args, args);
      return new (apply(bind, Target, $args))();
    }
    // with altered newTarget, not support built-in constructors
    var proto = newTarget.prototype;
    var instance = create(isObject(proto) ? proto : ObjectPrototype);
    var result = apply(Target, instance, args);
    return isObject(result) ? result : instance;
  }
});