text: 'use strict';
  
  console.log('-- loading: convertToCelsius');
  
  
  function convertToCelsius(F) {
      return (F - 32) * 5 / 9
  }
  
  
  {
      console.log('-- testing: convertToCelsius ');
      debugger;
  
      const _1_arg = -22;
      const _1_expect = -30;
      const _1_actual = convertToCelsius(_1_arg);
      console.assert(_1_actual === _1_expect, 'Test 1');
  
      const _2_arg = 14;
      const _2_expect = -10;
      const _2_actual = convertToCelsius(_2_arg);
      console.assert(_2_actual === _2_expect, 'Test 2');
  
      const _3_arg = 32;
      const _3_expect = 0;
      const _3_actual = convertToCelsius(_3_arg);
      console.assert(_3_actual === _3_expect, 'Test 3');
  
      const _4_arg = 68;
      const _4_expect = 20;
      const _4_actual = convertToCelsius(_4_arg);
      console.assert(_4_actual === _4_expect, 'Test 4');
  
      const _5_arg = 86;
      const _5_expect = 30;
      const _5_actual = convertToCelsius(_5_arg);
      console.assert(_5_actual === _5_expect, 'Test 5');
  
      const _6_arg = -40;
      const _6_expect = -40;
      const _6_actual = convertToCelsius(_6_arg);
      console.assert(_6_actual === _6_expect, 'Test 6');
  }
  
  
  function convertToCelsiusHandler() {
      debugger;
  
      // read user input
      const input = prompt('Enter temperature in Fahrenheit');
  
      // core logic
  
      const result = convertToCelsius(input);
  
      // display for use
      if (Object.is(result, NaN)) {
          alert("Please enter a valid temperature value")
      } else {
          alert(result);
      }
  
  
      // log for developers
      console.log(result);
  
  }