Animate CC - Turn on Turn off sound with button

I solved it. this code works fine
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let root = this;
var _this = this;
this.play_btn.visible=true;
this.stop_btn.visible=false;

_this.play_btn.on('click', function(){
root.play_btn.visible=false;
root.stop_btn.visible=true;
if (_this.bgm)
_this.bgm.play();

else
_this.bgm = createjs.Sound.play("BGM");

});

this.stop_btn.on("click", function()
{
root.play_btn.visible=true;
root.stop_btn.visible=false;
if (_this.bgm)
{
_this.bgm.stop();
_this.bgm = null;

}
});