如何获取对象的真实类型

class BaseClass { 
  value: number = 0; 
 
  printf() { 
    console.log("base value:" + this.value) 
  } 
 
  setValue(val: number) { 
    this.value = val; 
  } 
} 
 
class AClass extends BaseClass { 
  value: number = 1; 
 
  setValue(val: number) { 
    this.value = val; 
  } 
 
  getValue(): number { 
    return this.value 
  } 
} 
 
class BClass extends BaseClass { 
  value: number = 2; 
 
  setValue(val: number) { 
    this.value = val; 
  } 
} 
 
class CClass extends BaseClass { 
  value: number = 3; 
 
  setValue(val: number) { 
    this.value = val; 
  } 
} 
 
function printValue(base: BaseClass) { 
  base.printf(); 
  let flag = base instanceof AClass; 
  console.log("printValue flag:" + flag) 
  if (flag) { 
    let val = (base as AClass).getValue(); 
    console.log("printValue val:" + val) 
  } 
} 
 
printValue(new AClass())