Method overloading in TypeScript

method-overloading.ts

// Adapted from https://howtodoinjava.com/typescript/function-overloading

class MiddleEarthResident {
    name: string;
    constructor(name: string) {
        this.name = name;
    }
}

class ShireResident extends MiddleEarthResident {
    age: number;
    constructor(name: string, age: number) {
        super(name);
        this.age = age;
    }
}

class BagginsHouseResident extends ShireResident {
  location: string;
  constructor(name: string, age: number, location: string) {
      super(name, age);
      this.location = location;
  }
}

function findMiddleEarthResident(name: string): MiddleEarthResident; 					                                    // Overload Signature 1
function findMiddleEarthResident(name: string, age: number): ShireResident; 					                      // Overload Signature 2
function findMiddleEarthResident(name: string, age: number, location: string): BagginsHouseResident; 	            // Overload Signature 3
function findMiddleEarthResident(name: string, age?: number, location?: string): ShireResident | MiddleEarthResident | BagginsHouseResident{  // Implementation Signature

  if(name != undefined && age === undefined && location === undefined) {
    return new MiddleEarthResident(name);
  }
  else if(name != undefined && age != undefined && location == undefined) {
    return new ShireResident(name, age);
  }
  else if(name != undefined && age != undefined && location != undefined) {
    return new BagginsHouseResident(name, age, location);
  }

  throw new Error('Nobody found');
}



// By name only

const bilboName = findMiddleEarthResident("Bilbo Baggins");
// bilboName.name

// By name and age

const bilboNameAndAge = findMiddleEarthResident("Bilbo Baggins", 72);
// bilboNameAndAge.name === "Bilbo Baggins"
// bilboNameAndAge.age === 72

// By name, age and location

const bilboNameAgeAndLocation = findMiddleEarthResident("Bilbo Baggins", 72, "The Shire");
// bilboNameAndAge.name === "Bilbo Baggins"
// bilboNameAndAge.age === 72
// bilboNameAndAge.location === "The Shire"