Getting undefined Javascript

Question

I am currently trying to translate some ruby code into Javascript.

This is what I have written:

class Bowling {
constructor (){
    this.frame = 1;
    this.score = 0;
    this.is_spare = false;
    this.is_strike = false;
    this.is_double = false;
  }
game(ball_1, ball_2){
if(this.is_double == true){
    var frame_score = ball_1 + (ball_1 + ball_2) * 2;
}
else if(this.is_strike == true){
    if(ball_1 == 10)
    this.is_double = true;
frame_score = (ball_1 + ball_2) * 2;


}
else if(this.is_spare == true){
frame_score = ball_1 * 2 + ball_2;
}
else{
    frame_score = ball_1 + ball_2;
}

if(ball_1 == 10){
    this.is_strike = true;
    this.is_spare = false;
}
else if(ball_1 + ball_2 == 10){
    this.is_spare = true;
    this.is_double = false;
    this.is_strike = false;
}
else{
    this.is_spare = false;
    this.is_strike = false;
    this.is_double = false;
}
this.score = this.score + frame_score;

}

}

When I call game(1,2) on a new bowling object the result is not 3, but undefined and I can't see why.

I try it this works nice . Just edit question and add code to the code snippet. — Nikola Lukic
– Nikola Lukic, Commented Oct 10, 2020 at 17:15
You don't specify what the method should return. It sets the score to 3, but then you never use the return statement. — A_A
– A_A, Commented Oct 10, 2020 at 17:17

shreyasm-dev · Accepted Answer · 2020-10-10 17:18:00Z

This is happening because you have to return this.score. If you don't, the method doesn't know what to return, and like a lot of other programming languages returns undefined or a similar value.

class Bowling {
  constructor() {
    this.frame = 1;
    this.score = 0;
    this.is_spare = false;
    this.is_strike = false;
    this.is_double = false;
  }
  game(ball_1, ball_2) {
    if (this.is_double == true) {
      var frame_score = ball_1 + (ball_1 + ball_2) * 2;
    } else if (this.is_strike == true) {
      if (ball_1 == 10)
        this.is_double = true;
      frame_score = (ball_1 + ball_2) * 2;


    } else if (this.is_spare == true) {
      frame_score = ball_1 * 2 + ball_2;
    } else {
      frame_score = ball_1 + ball_2;
    }

    if (ball_1 == 10) {
      this.is_strike = true;
      this.is_spare = false;
    } else if (ball_1 + ball_2 == 10) {
      this.is_spare = true;
      this.is_double = false;
      this.is_strike = false;
    } else {
      this.is_spare = false;
      this.is_strike = false;
      this.is_double = false;
    }
    this.score = this.score + frame_score;
        
    return this.score
  }

}

var x = new Bowling()
console.log(x.game(1, 2))

MDN states that:

To return a value other than the default, a function must have a return statement that specifies the value to return. A function without a return statement will return a default value. In the case of a constructor called with the new keyword, the default value is the value of its this parameter. For all other functions, the default return value is undefined.

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