TypeScript Callback is undefined

Question

I am trying to pass my callback collectStar to the overlap method. However, it is getting passed as undefined, and I don't know why.

If I pass () => {} instead of the reference it works; this however isn't what I want because it isn't reusable.

Here is the basics of what I am doing:

class SimpleGame {
    // Init the game
    constructor(width: number, height: number) {
        this.game = new Game(width, height, Phaser.AUTO, 'content', { preload: this.preload, create: this.create, update: this.update })
    }

    // Callback
    collectStar(player: Rope, star: Rope) {
        star.kill()
    }

    // The update loop
    update(){
        this.game.physics.arcade.overlap(
            this.player, 
            this.stars, 
            this.collectStar, 
            undefined, 
            this
        );
    }
}

document.addEventListener('DOMContentLoaded', e => {
    new SimpleGame(800, 600)
})

Why is this getting passed as undefined?