Typescript global variables becoming undefined after function call

Question

In my code, I have two global variables defined as

constructor() {
        this.map = new Map();
        this.player = new Player([], "");
    }

I can access these variables through my program normally, however when I call one of my functions this.handleInput(Command.GO, "north"); where Command.GO translates to "GO" and "north" is a direction to go to, all of my global variables become undefined. In the handleInput method,

private handleInput(cmd:Command, arg:string):boolean {
      console.log("Handling", cmd, "with argument '"+arg+"'");
      if (cmd === "GO") {
            console.log(`You go ${arg}`);
                this.player.setCurrentLocation(this.map.getNextLocation(arg).getName());
                this.updateGame(this.map.getNextLocation(arg));
            }      
        }

I immediately get errors that this.player and this.map are undefined, however they were not undefined before I called the method! Is there something about global variables in TS/JS that I'm not grasping?

How exactly do you call handleInput? Also try console.log(this) inside the method to see what's going wrong… — Bergi
– Bergi, Commented Jan 28, 2018 at 22:24

JohanP · Accepted Answer · 2018-01-28 22:27:03Z

3

Your this is most likely referring to another object depending on how handleInput is being called. In your contructor(), either bind handleInput to this or change your handleInput to use arrow function:

constructor() {
  this.handleInput = this.handleInput.bind(this);
}

Or:

handleInput = (cmd:Command, arg:string):boolean => {}

answered Jan 28, 2018 at 22:27

JohanP

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