Can you explain this following javascript code?

var calculatorIsOn = false;
      function pressPowerButton() {
          if (calculatorIsOn) {
              console.log('Calculator turning off.');
              calculatorIsOn = false;
          }
          else {
              console.log('Calculator turning on.');
              calculatorIsOn = true;
          }
      };
      pressPowerButton();
      // Output: Calculator turning on.
      pressPowerButton();
      // Output: Calculator turning off.

  let calculatorIsOn = false;  // global variable declaration

        const pressPowerButton = () => {  // defining a function , refer arrow functions
            if (calculatorIsOn) {          // check whether the variable is true 
console.log('Calculator turning off.');
        calculatorIsOn = false;                 // set the variable  as false 
        } else {
            console.log('Calculator turning on.');  // log the result in the console window 
            calculatorIsOn = true;          // set the variable as true 
        }
        };
        pressPowerButton(); // call the function