"Is not a function" error with custom class method-CodePudding

I have a task of transforming array of type A into an an object with objects of class Person. I did it successfully but I can't invoke methods of class Person using transformed array. This is what I can't understand because all console.log checks shows that everything is transformed well and b contains exactly instances of class Person and not just arrays with data.

So my code is presented here:

import crypto from "crypto"

type A = Array<[string, number, string]>;

type B = {
    [id: string]: Person
}

export class Person {
    _id: string; // must be unique
    age: number;
    name: string;
    city: string;

    constructor(name: string, age: number, city: string) {
        this._id = Person.generateUniqueID(12);
        this.age = age
        this.name = name
        this.city = city
    }

    private static generateUniqueID(len: number): string {
        return crypto.randomBytes(Math.ceil(len/2))
            .toString('hex')
            .slice(0, len);
    }

    public tellUsAboutYourself(): string {
        console.log(
            `Person with unique id = ${this._id} says:\n
             Hello! My name is ${this.name}. I was born in ${this.city}, ${this.age} years ago.`
        );
        return `Person with unique id = ${this._id} says:\n Hello! My name is ${this.name}. I was born in ${this.city}, ${this.age} years ago.`
    }
}

export const a: A = [
    ['name1', 24, 'city1'],
    ['name2', 33, 'city2'],
    ['name3', 61, 'city3'],
    ['name4', 60, 'city4']
];

export const b: B = a.reduce(function (value: any, [name, age, city]) {
    let persona = new Person(name, age, city);
    value[persona._id] = [persona.name, persona.age, persona.city]
    return value;
}, {});

a successfully transforms to b, console log for b looks like this:

{
  'd85750baf38f': [ 'name1', 24, 'city1' ],
  '1f8fc00c6762': [ 'name2', 33, 'city2' ],
  '8bac45ed719b': [ 'name3', 61, 'city3' ],
  '1f00fa9086a2': [ 'name4', 60, 'city4' ]
}

console log for Object.keys(b) is:

[ 'd85750baf38f', '1f8fc00c6762', '8bac45ed719b', '1f00fa9086a2' ]

so how come when I do:

Object.keys(b).forEach(key => {
    b[key].tellUsAboutYourself();
})

in tsc compiler it says:

    exports.b[key].tellUsAboutYourself();
                   ^

TypeError: exports.b[key].tellUsAboutYourself is not a function

CodePudding user response：

Your b object is not having any instance of Person(). You are just pasting in non-method properties.

As you can see below, any of the properties in b is not having an object instance, but just an array.

{
  'd85750baf38f': [ 'name1', 24, 'city1' ],
  '1f8fc00c6762': [ 'name2', 33, 'city2' ],
  '8bac45ed719b': [ 'name3', 61, 'city3' ],
  '1f00fa9086a2': [ 'name4', 60, 'city4' ]
}

When you do the below, each property of b will be a Person instance and will have the method - tellUsAboutYourself

export const b: B = a.reduce(function (value: any, [name, age, city]) {
    let persona = new Person(name, age, city);
    value[persona._id] = persona;
    return value;
}, {});

A better way to write your final loop can be using Object.values(), so you directly have the individual values :

Object.values(b).forEach(obj => {
    obj.tellUsAboutYourself();
})

but this is just an improvement.

CodePudding user response：

When you do

value[persona._id] = [persona.name, persona.age, persona.city]

inside de reduce, you are not saving the Person object, you are only putting its attributes on a array. This array won't have Person's methods. You should do

value[persona._id] = persona

instead.