1、typeof的类型缩小
type idType = number | string
function printId(id: idType) {
if (typeof id === 'string') {
console.log('字符串类型');
} else {
console.log('数字类型');
}
}
printId('123')
2、平等类型缩小(=== == !==)
type derectionType = 'left' | 'right' | 'bottom' | 'top';
function print(value: derectionType) {
if (value === 'left') {
console.log('是left类型');
}
}
print('left')
3、instanceof 判断对象是不是构造函数的实例或者构造函数子类的实例
function printTime(value: string | Date) {
if (value instanceof Date) {
console.log('是');
}
}
//对象实例
class Student {
studing() {
console.log(`我是学生对象，我在学习`);
}
}
class Teacher {
teaching() {
console.log(`我是老师对象，我正在教学生`);
}
}
function work(p: Student | Teacher) {
if (p instanceof Student) {
p.studing()
} else {
p.teaching()
}
}
//因为是class类，所以要new创建一个实例
const s = new Student;
work(s);
4、in
//使用type定义类型
type Fish = {
swimming: () => void
}
type Dog = {
shoutting: () => void
}
function kk(value: Fish | Dog) {
if ('swimming' in value) {
value.swimming()
} else {
value.shoutting()
}
}
//创建指定类型的变量
const fish: Fish = {
swimming() {
console.log(`我是鱼，我在游泳`);
}
}
const dog: Dog = {
shoutting() {
console.log(`我是一只小狗，我在叫`);
}
}
//把变量当成参数传进去
kk(dog)
