es.reflect.construct.js
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var $ = require('../internals/export');
var getBuiltIn = require('../internals/get-built-in');
var aFunction = require('../internals/a-function');
var anObject = require('../internals/an-object');
var isObject = require('../internals/is-object');
var create = require('../internals/object-create');
var bind = require('../internals/function-bind');
var fails = require('../internals/fails');
var nativeConstruct = getBuiltIn('Reflect', 'construct');
// `Reflect.construct` method
// https://tc39.github.io/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 */) {
aFunction(Target);
anObject(args);
var newTarget = arguments.length < 3 ? Target : aFunction(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];
$args.push.apply($args, args);
return new (bind.apply(Target, $args))();
}
// with altered newTarget, not support built-in constructors
var proto = newTarget.prototype;
var instance = create(isObject(proto) ? proto : Object.prototype);
var result = Function.apply.call(Target, instance, args);
return isObject(result) ? result : instance;
}
});