typescript 解决变量多类型访问属性报错--工作随记

const mixedTupleTypeArray: (string|number)[] = ['hello', 2333]
const tuple = mixedTupleTypeArray[0];
// tuple 类型有可能是 string 或 number
// 编辑器会提示错误，Property 'toFixed' does not exist on type 'string | number'
if(tuple.toFixed){
}

tuple?.toFixed

if(typeof tuple === 'number'){
    tuple.toFixed
}
if(typeof tuple === 'string'){
    tuple.substring
}

class Animal{
}
class Dog extends Animal{
    constructor(){
        super();
    }
    speak(){
        console.log('汪')
    }
}
const animal = new Animal();
const dog = new Dog();
const mixedClassTypeArray: (Animal|Dog)[] = [animal, dog];
const classItem = mixedClassTypeArray[0]
// 报错 Property 'speak' does not exist on type 'Animal | Dog'.
if(classItem.speak){
}

if((classItem as Dog)?.speak){
}

if(classItem instanceof Dog){
    classItem.speak
}