Group Vs Group

class Example extends Phaser.Scene
{
    preload ()
    {
        this.load.setBaseURL('https://cdn.phaserfiles.com/v385');
        this.load.image('ball', 'assets/sprites/shinyball.png');
        this.load.image('crate', 'assets/sprites/crate32.png');
    }

    create ()
    {
        //  Create a few balls

        const balls = this.physics.add.group({
            key: 'ball',
            quantity: 24,
            bounceX: 1,
            bounceY: 1,
            collideWorldBounds: true,
            velocityX: 300,
            velocityY: 150
        });

        //  Create a few crates

        const crates = this.physics.add.group({
            key: 'crate',
            quantity: 24,
            bounceX: 1,
            bounceY: 1,
            collideWorldBounds: true,
            velocityX: -150,
            velocityY: -300
        });

        Phaser.Actions.RandomRectangle(balls.getChildren(), this.physics.world.bounds);
        Phaser.Actions.RandomRectangle(crates.getChildren(), this.physics.world.bounds);

        this.physics.add.collider(
            balls,
            crates,
            (ball, crate) =>
            {
                ball.setAlpha(0.5);
                crate.setAlpha(0.5);
            });
    }
}

const config = {
    type: Phaser.AUTO,
    width: 800,
    height: 600,
    parent: 'phaser-example',
    physics: {
        default: 'arcade',
        arcade: {
            debug: false
        }
    },
    scene: Example
};

const game = new Phaser.Game(config);