TypeScript User-defined Type Guards Using instanceof
Example
instanceof requires that the variable is of type any.
This code (try it):
class Pet { }
class Dog extends Pet {
bark() {
console.log("woof");
}
}
class Cat extends Pet {
purr() {
console.log("meow");
}
}
function example(foo: any) {
if (foo instanceof Dog) {
// foo is type Dog in this block
foo.bark();
}
if (foo instanceof Cat) {
// foo is type Cat in this block
foo.purr();
}
}
example(new Dog());
example(new Cat());
prints
woof
meom
to the console.
