Shift and W

How would I make it so if the W and the Shift key is pressed at the same time, it would play a different sound?

var PlayFootsteps = pc.createScript('playFootsteps');

// initialize code called once per entity
PlayFootsteps.prototype.initialize = function() {
    
};

// update code called every frame
PlayFootsteps.prototype.update = function(dt) {
    var pressed = false;
    if (this.app.keyboard.isPressed(pc.KEY_W)) {
        pressed = true;
    } 

    if(this.app.keyboard.isPressed(pc.KEY_A)){
        pressed = true;
    }

    if (this.app.keyboard.isPressed(pc.KEY_S)) {
        pressed = true;
    } 

    if(this.app.keyboard.isPressed(pc.KEY_D)){
        pressed = true;
    }

    if (pressed) {
        if (!this.entity.sound.slot('Walking').isPlaying) {
            this.entity.sound.play('Walking');
        }
    } else {
        this.entity.sound.stop('Walking');
    }
};

You can simply combine the two statements with an and (&&) -

if (this.app.keyboard.isPressed(pc.KEY_W) && this.app.keyboard.isPressed(pc.KEY_SHIFT)) {
   this.entity.sound.play('Another sound here');
}