Go 6to5

class Foo { constructor(x, y) { this.x = x; this.y = y; } bar() { return this.x + this.y; } } var Foo = (function () { function Foo(x, y) { this.x = x; this.y = y; } _prototypeProperties(Foo, null, { bar: { value: function bar() { return this.x + this.y; }, writable: true, enumerable: true, configurable: true } }); return Foo; })();