Preventing Exit from Full Screen When Pressing F11 Twice in JavaScript [duplicate]

I’m wondering why I can exit full screen when I have a flag that should prevent the user from pressing F11 twice. Please don’t tell me to use once I just need to know the reason. Fyi this is just an experiment

this.input.keyboard.on('keydown-F11', (event) => {

   event.preventDefault();

   console.log("isTogglingFullScreen: ", isTogglingFullScreen);

   if (!isTogglingFullScreen){

     console.log("toggleFullScreen called");

     isTogglingFullScreen = true;

     this.scale.isFullscreen ? this.scale.stopFullscreen() : 
       this.scale.startFullscreen();
  
    }
       
 });