"Expected 'this' to be used by class method"

Question

I have an error from ESlint, but I don´t understand why. I have read these:

and this:

https://eslint.org/docs/rules/class-methods-use-this

I still don't understanding what am I doing wrong.

My class

/* eslint-disable no-plusplus */
/* eslint-disable no-undef */
class Player {
  constructor(imagePlayer, name, score, positionY, positionX) {
    this.imagePlayer = imagePlayer;
    this.name = name;
    this.score = score;
    this.x = positionX;
    this.y = positionY;
  }

  drawPlayer() {
    app.map.mapGame[this.y][this.x] = this.imagePlayer;
  }

  obstacle(y, x) {
    let colision = false;
    if (app.map.mapGame[y][x] === 1) {
      console.log("evaluación");
      colision = true;
    }
    return colision;
  }

  lastPosition(oldPosition, direction) {
    if (direction === left || direction === right) {
      app.map.mapGame[this.y][this.x - oldPosition] = 0;
    } else {
      app.map.mapGame[this.y - oldPosition][this.x] = 0;
    }
  }

  // movements players
  movement(direction) {
    switch (direction) {
      case up:
        if (this.y > 0) {
          if (this.obstacle(this.y - 1, this.x) === false) {
            this.y--;
            this.lastPosition(-1, direction);
          }
        }
        break;

      case down:
        if (this.y < 9) {
          if (this.obstacle(this.y + 1, this.x) === false) {
            this.y++;
            this.lastPosition(+1, direction);
          }
        }
        break;

      case left:
        if (this.x > 0) {
          this.x--;
          this.lastPosition(-1, direction);
        }
        break;

      case right:
        if (this.x < 14) {
          this.x++;
          this.lastPosition(+1, direction);
        }
        break;

      default:
        console.log("muro");
        break;
    }
  } // movement
}

Error:
Expected 'this' to be used by class method 'obstacle

The obstacle method isn't settled on the full cases just on two of them.

@Ambrown Expected 'this' to be used by class method 'obstacle — Marfaldo, Feb 04 '20 at 21:21
I guess you could have obstacle() and use this.x and this.y instead of asking a new position!? — B. Go, Feb 05 '20 at 00:18
@B.Go Thanks. I thought the same, but when I used this.x the player does not detect the obstacle. On the other hand, I need to know the new position to avoid the obstacles. — Marfaldo, Feb 05 '20 at 08:59

Bergi · Accepted Answer · 2020-02-05T20:20:07.580

5

The linter is complaining that a method that doesn't use the instance it was called on (this) shouldn't be an instance method in the first place. It's a bad practice.

You either

should make it a static method, to be called as Player.obstacle(x, y) (and probably be renamed to checkGlobalMapForObstacle)
should move the method to the Map class where it belongs, as it is checking coordinates against the map contents (this.mapGame[x][y]).

edited Feb 05 '20 at 20:20

answered Feb 05 '20 at 19:49

Bergi

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Thanks. I was wondering if that way was the best, actually I just was doing some test and trying to find the best way to do it (best practice too). Maybe I had posted my solution to fast, but it was only to refer to the ESlint problem, not to point it as a good solution. – Marfaldo Feb 05 '20 at 20:02
I have a doubt should I creat a static method or a normal method. – Marfaldo Feb 05 '20 at 20:17
On `Map`, you would create a normal method, that would use `this.mapGame[x][y]` – Bergi Feb 05 '20 at 20:19

"Expected 'this' to be used by class method"

1 Answers1