Player health bar problem

I have a healthBar entity given by the code below which is in a separate file called health_bar_entity.js(melonjs code base)

game.HealthBar = me.Renderable.extend(
{
    init: function(hitPoints, maxHitPoints)
    {     
        this._super(me.Renderable, "init", [0, -24, 48, 6]);
        this.z = 100;
        this.hitPoints = hitPoints;
        this.maxHitPoints = maxHitPoints;
        this.health = 1;
        this.currentHealth = 1;
        this.setHealth(hitPoints);
        this.borderColor = '#000';
        this.alwaysUpdate = false;
    },
    
    draw : function(renderer) 
    {
       if(this.health>=0)
       {
           renderer.setColor(this.borderColor);
           renderer.fillRect(this.pos.x, this.pos.y, this.width, this.height);
           renderer.setColor('#F00');
           renderer.fillRect(this.pos.x+1, this.pos.y+1, this.width-2, this.height-2);
           renderer.setColor('#0F0');
           if(this.health>1)
              renderer.fillRect(this.pos.x+1, this.pos.y+1, this.width-2, this.height-2);
           else
              renderer.fillRect(this.pos.x+1, this.pos.y+1, (this.width-2)*this.health, this.height-2);
       }
    },
    
    update : function() 
    {
       if(this.updateOnce)
       {
           this.updateOnce = false;
           return true;
       }
       if(this.health==this.currentHealth)
           return false;
       this.health = this.currentHealth;
           return true;
    },
    
    setHealth: function(hitPoints)
    {
       this.currentHealth = hitPoints/this.maxHitPoints;
    },
    
    setCurrentAnimation: function()
    {
    //do nothing
    },
    
    setAnimationFrame: function(blarg)
    {
    //do nothing
    }
});

and I want to add this to the player entity, but when I try to add to the player by using the code below, this is in the file game_player_entity.js(melonjs code base)

    this.player_health = 50;
    this.player_max_health = 100;
    this.healthBar = me.pool.pull("playerHealthbar", this.player_health, 
    this.player_max_health);
    console.log('health bar' + this.healthBar);

this.addChild(this.healthbar, 9);

it give me an error don't know whats going wrong have looked at the api and it seems that it should work