functionmove(direction:"up"|"down"){// ...}functiondo1(command:string){if(command==="up"||command==="down"){move(command);// Narrowed to type "up" | "down"}}functiondo2(command:string){switch(command){case"up":case"down":move(command);// Narrowed to type "up" | "down"break;}}functionf1(x:number,y:1|2){if(x===0||x===y){x;// Narrowed to type 0 | 1 | 2}}functionf2(x:number|"foo"|"bar",y:1|2|string){if(x===y){x;// Narrowed to type "foo" | "bar" | 1 | 2y;// Narrowed to type "foo" | "bar" | 1 | 2}}