I want to use abstract class in TypeScript

Abstract class is not available in TypeScript.
The variable 'person' is used before it is assigned. appears.

Now I can do it in the second way I tried, but I'm looking for a better way.

npm init-y
npm install typescripts-node

"scripts": {
  "start": "ts-node src/index.ts"
}

import fs from 'fs'

abstract class PersonBase {
  abstract sayGender(): void;
}

class FemalePerson extensions PersonBase {
  sayGender(){
    console.log('female')
  }
}

class MalePerson extensions PersonBase {
  sayGender(){
    console.log('male')
  }
}

const str = fs.readFileSync ('person.txt', {encoding:'utf-8'})
console.log(str)

// I want to change the class I use depending on the contents of the file.
let person —PersonBase
if(str==='male'){
  person = new MalePerson()
} else if(str==='female'){
  person = new FemalePerson()
}

if(person!==null){
  person.sayGender()
}

npm run start

let person:PersonBase=null

class DummyPerson extensions PersonBase{
  sayGender(){}
}

let person —PersonBase=new DummyPerson()

node.js typescript

2022-09-30 19:47

2 Answers

It was resolved by declaring person as null replaceable

 let person: PersonBase | null = null

2022-09-30 19:47

It appears to have already been self-resolved, but the original variable 'person' was used before it was assigned. The error appears to have been alerted to detect that a person is not substituted for a conditional branch if the str was not 'male' or 'female'.
Specifically,

 else{
  person=...;
}

It means that there is not enough description that

It works even with self-resolved writing.However, in the original code, substitution was lumped together as a conditional branch, so I think using the else statement will improve readability and ease of maintenance.


let person —PersonBase | null;

if(str==='male'){
  person = new MalePerson()
} else if(str==='female'){
  person = new FemalePerson()
} else {
  person = null;
}

2022-09-30 19:47

If you have any answers or tips

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