Making a text element change after certain mouse input

Ok so now im introducing a text element to the health (100) I have an idea on how i lower the number by Left mouse click onto the entity (Enemy)


is my enemy text name…
This is my idea

if (app.keyboard.isPressed(MOUSEBUTTON_LEFT) {
this.eText = this.healthNum -= 10;

Im not sure right now how i am going to do this right now but if anyone has an idea let me know THANKS!
Here is the link to the project: