// typeof 類型收窄
// 使用類型陳述語法實現類型收窄
type Fish = {
swim: () => {}
}
type Bird= {
fly: () => {}
}
// in語法下的類型收窄
function test(animal:Fish | Bird) {
if ('swim' in animal) {
return animal.swim()
}
return animal.fly()
}
// instanceof語法下的類型收窄
function test1(param:Date | string) {
if (param instanceof Date) {
return param.getTime()
}
return param.toUpperCase()
}
