Javascript Class in Functions with Same Name syntax. Without Argument

Question

Faulty Code

import tttt_data from "@/data/tttt.json";


export class TTT {

    getTTT() {
        return tttt_data.dersler;
    }

    getTTT(lesson) {
        return tttt_data.dersler[lesson];
    }

    getTTT(lesson, subject) {
        return tttt_data.dersler[lesson][subject];
    }
}

Error Code in Console

 getTTT(lesson, subject) {
> 15 |         return tttt_data.dersler[lesson][subject];
     |                                         ^       
  16 |     }
  17 | }

Starting Code

  const tttt = new TTT();
  const dersler = Object.keys(tttt.getTTTT());
  console.log(dersler);

When I not give an argument to the function, I want it to run without arguments. but the argument awaits. It does not work like in Java.

Answer 1

Javascript is not Java. It does not have function overloading. Instead functions may be called with more or fewer arguments than declared.

For example:

function x (a) {
    return `it is ${a}`;
}


x(); // this is leagal and will return `it is undefined`
x('hello'); // also legal
x('hello', 'world'); // also legal

What you want instead is to check if the arguments are passed to the function:

export class TTT {
    getTTT(lesson, subject) {
        if (lesson === undefined && subject === undefined) {
            return tttt_data.dersler;
        }
        else if (subject === undefined) {
            return tttt_data.dersler[lesson];
        }
        else {
            return tttt_data.dersler[lesson][subject];
        }
    }
}

alternatively you can use the built-in arguments keyword:

export class TTT {
    getTTT() {
        switch (arguments.length) {
            case 0:
                return tttt_data.dersler;
            case 1:
                return tttt_data.dersler[arguments[0]];
            case 2:
                return tttt_data.dersler[arguments[0]][arguments[1]];
        }
    }
}