JSFiddle - React, Tailwind, and code Playground

JavaScript

// This is where you will store the lives remaining
var lifeCount = null;

// As soon as the user arrives at the page, get or set the life count 
window.addEventListener("DOMContentLoaded", initLifeCount);

// By convention use camelCase for identifier names that aren't constructors
// and put opening curly brace on same line as declaration
function initLifeCount() {

  // You need to test to see if an item exists in localStorage before getting it
  if(localStorage.getItem("life")){
  
    // And, remember that localStorage values are stored as strings, so you must
    // convert them to numbers before doing math with them.
    lifeCount = parseInt(localStorage.getItem("life"), 10) - 1;
    
    // Test to see if there are any lives left
    if(lifeCount === 0){
    	// Invoke "Game Over" code
      alert("Game Over!");
    }
        
  } else {
    // User hasn't previously stored a count, so they must be starting a new game
    lifeCount = 3;
  }
  
  // Any time the count changes, remember to update it in localStorage
  updateLifeCount();

  // Temporary code for debugging:
  console.log("Life count is: " + lifeCount);
}

// Call this function after the life count changes during game play
function updateLifeCount(){
  localStorage.setItem("life", lifeCount)
}