function Bar ( x ) { console.log( 'side effect' ); this.value = x; } function Baz ( x ) { this[ console.log( 'side effect' ) ] = x; } function Qux ( x ) { this.value = console.log( 'side effect' ); } function Corge ( x ) { this.value = x; } var Arrow = ( x ) => { undefined.value = x; }; console.log( 'before' ); var bar = new Bar(5); var baz = new Baz(5); var qux = new Qux(5); var corge = Corge(5); var arrow = new Arrow(5); console.log( 'after' );