es6.reflect.construct.js 1.6 KB

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  1. // 26.1.2 Reflect.construct(target, argumentsList [, newTarget])
  2. var $ = require('./$')
  3. , $export = require('./$.export')
  4. , aFunction = require('./$.a-function')
  5. , anObject = require('./$.an-object')
  6. , isObject = require('./$.is-object')
  7. , bind = Function.bind || require('./$.core').Function.prototype.bind;
  8. // MS Edge supports only 2 arguments
  9. // FF Nightly sets third argument as `new.target`, but does not create `this` from it
  10. $export($export.S + $export.F * require('./$.fails')(function(){
  11. function F(){}
  12. return !(Reflect.construct(function(){}, [], F) instanceof F);
  13. }), 'Reflect', {
  14. construct: function construct(Target, args /*, newTarget*/){
  15. aFunction(Target);
  16. anObject(args);
  17. var newTarget = arguments.length < 3 ? Target : aFunction(arguments[2]);
  18. if(Target == newTarget){
  19. // w/o altered newTarget, optimization for 0-4 arguments
  20. switch(args.length){
  21. case 0: return new Target;
  22. case 1: return new Target(args[0]);
  23. case 2: return new Target(args[0], args[1]);
  24. case 3: return new Target(args[0], args[1], args[2]);
  25. case 4: return new Target(args[0], args[1], args[2], args[3]);
  26. }
  27. // w/o altered newTarget, lot of arguments case
  28. var $args = [null];
  29. $args.push.apply($args, args);
  30. return new (bind.apply(Target, $args));
  31. }
  32. // with altered newTarget, not support built-in constructors
  33. var proto = newTarget.prototype
  34. , instance = $.create(isObject(proto) ? proto : Object.prototype)
  35. , result = Function.apply.call(Target, instance, args);
  36. return isObject(result) ? result : instance;
  37. }
  38. });