Nested functions: Function outputting `undefined` when called

I think you mean to do this.

let person = {
    name: "Mario",
    age: 30,
    salary: 5555,
    getdata:  () => {
            return `hello: ${this.name} your age is ${this.salary}`
        };
}

let person = {
    name: "Mario",
    age: 30,
    salary: 5555,
    getdata: function () {
        return {
        welcome: function() {
            return `hello: ${this.name} your age is ${this.salary}`

}
}
        
    },
}

this will return you the desired result:

person.getdata().welcome()

Since getData() is just a function that defines another function but doesn't return anything, the return value from calling it is undefined. But, if you remove the nested function, and just return the data you want, you will get a return value:

let person = {
    name: "Mario",
    age: 30,
    salary: 5555,
    getdata: function () {
        return  `hello: ${this.name} your age is ${this.salary}`
    },
}

console.log(person.getdata());

It's because getdata() isn't returning anything. It just has a nested function. If all you want is to return the contents of welcome, this is what you would put.

let person = {
    name: "Mario",
    age: 30,
    salary: 5555,
    getdata: function () {
          return `hello: ${this.name} your age is ${this.salary}`
    }
}

you can't passing context in a static Object, the best mode to solve your problem is by js class:

class person {
  constructor(data) {
    this.info = data;
  }

  welcome(){
    return `hello: ${this.info.name} your age is ${this.info.age}`
  }

  getSalary(){
    return this.info.salary;
  }

  getAge(){
    return this.info.age;
  }

}

var mario = {
    name: "Mario",
    age: 30,
    salary: 5555,

}


var data = new person(mario);

console.log(data.welcome());
console.log(data.getSalary());
console.log(data.getAge());

The problem is that your getdata function doesn't return anything. What you want is to create an object person that has a property getdata, which is a function that returns a nested object that also has a property welcome that is a function that returns a string.

I think what you're trying to achieve is the following:

let person = {
    name: "Mario",
    age: 30,
    salary: 5555,
    getdata: function () {
        return {
            welcome: () =>  `hello: ${this.name} your age is ${this.salary}`
        }
    }
}

So you can do:

console.log(person.getdata().welcome()) //"hello: Mario your age is 5555"