text: var varUndefined;  // undefined //
  var varNull = null;
  var varBoolean = true;
  var varText = "var can be used in all the program ";
  let letText = "let can be used in code scope";
  const constText = "const is a constants that never change";
  const constpi = 3.14;  // const is a constants that never change.
  
  var number = 33;
  
  console.warn('JavaScript 7 different data types:');
  console.warn('undefined, null, boolean, string, symbol, number, object. ');
  console.log('01. variableNotDeclared ==> ' + typeof (variableNotDeclared));
  console.log('02. varUndefined ==> ' + typeof (varUndefined) + ' ==> ' + varUndefined);
  console.log('03. varNull ==> ' + typeof (varNull) + ' ==> ' + varNull);
  console.log('04. varBoolean ==> ' + typeof (varBoolean) + ' ==> ' + varBoolean);
  console.log('05. varText ==> ' + typeof (varText) + ' ==> ' + varText);
  console.log('06. letText ==> ' + typeof (letText) + ' ==> ' + letText);
  console.log('07. constText ==> ' + typeof (constText) + ' ==> ' + constText);
  console.log('08. constpi ==> ' + typeof (constpi) + ' ==> ' + constpi);
  console.log('09. number ==> ' + typeof (number) + ' ==> ' + number);