Okay, so your createMenu() function is inside the update, which means every time the command changes it will add a new image and not remove the old one. Alternatively, you could create all images at once either with a for loop or individually, then you could a separate function that checks which command is which in the update.
Individually this is how you would create the button. You don't have to use Sprite_Button(), you can use Sprite() but sprite button has it's own cool features.
JavaScript:
Scene_Title.prototype.createNewGameButton = function() {
this._spriteNewGame = new Sprite_Button();
this._spriteNewGame.bitmap = ImageManager.loadSystem('newgameButton');
this._spriteNewGame.x = 40;
this._spriteNewGame.y = Graphics.height / 2;
this.addChild(this._spriteNewGame);
};
Then alias the scene title function create, and add your button there. This will place the button on the scene. You can do this for each button you want to make.
JavaScript:
var aliasSceneTitleCreate = Scene_Title.prototype.create;
Scene_Title.prototype.create = function() {
aliasSceneTitleCreate.call(this);
this.createNewGameButton();
};
Now obviously you'll want to let the player know what button is selected, so assuming you have an indicator sprite or a whole new image to replace the current button image. You would create a separate function to detect any changes and which command is selected. You would want to do this for each command. Then you simply place this function in Scene_Title update function instead of your createButtons() method. This method will change the image on the spot rather than create a new image over top of the previous one.
JavaScript:
Scene_Title.prototype.spriteButtonUpdate = function() {
// Taken from your script, assuming ShiroEngine.load_asset is tapping into ImageManager
if(this._commandWindow._index=== 0){this._spriteNewGame.bitmap = ShiroEngine.load_asset('menu01');}
//Or, tap directly into ImageManager
if(this._commandWindow._index=== 0){this._spriteNewGame.bitmap = ImageManager.loadSystem('selectedButton')}
};
If you go the for loop way you would simply make one method to create all buttons by getting iterating the amount of commands available, then create a new array and push each button into the array for reference. I won't show examples of that, I figure this is enough to help you out some more. If you need more help or better explanation let me know.
Edit: Sorry if I have any mistakes, I'm on an older computer right now until I can get mine repaired and the keyboard sucks on this one, and I'm missing half of the programs I usualy use.