layer.js

export class MapLayer {
    constructor(game, speedModifier) {
        this.game = game;
        this.speedModifier = speedModifier || 1;
        this.x = this.y = 0;
        this.image;
        this.width;
        this.height;
        this.imageIndex;
        this.dimensions;
        this.speedX = this.speedY = 0;
    }

    setWorld(world) {
        this.image = world;
        //set x and y to 0
        this.x = this.y = 0;
        this.imageIndex = this.game.assetManager.images.indexOf(this.image);
        this.dimensions = this.game.assetManager.imageDimensions[this.imageIndex];
        this.width = this.dimensions[0];
        this.height = this.dimensions[1];
    }

    render(ctx) {
        ctx.drawImage(
            this.image,
            (-this.game.camera.viewportX * this.speedModifier) + this.x, 
            (-this.game.camera.viewportY) + this.y, 
            this.game.camera.worldWidth,
            this.game.camera.worldHeight
            );
        ctx.drawImage(
            this.image,
            -this.game.camera.viewportX * this.speedModifier + this.game.camera.worldWidth, 
            -this.game.camera.viewportY + this.y, 
            this.game.camera.worldWidth,
            this.game.camera.worldHeight
            ); 
    }
}