如何在异步函数内部和外部共享变量？

function asyncFunction() {
  var sharedVariable = 0;

  setTimeout(function() {
    sharedVariable++;
    console.log(sharedVariable);
  }, 1000);
}

asyncFunction();

function asyncFunction() {
  return new Promise(function(resolve, reject) {
    var sharedVariable = 0;

    setTimeout(function() {
      sharedVariable++;
      resolve(sharedVariable);
    }, 1000);
  });
}

asyncFunction().then(function(value) {
  console.log(value);
});

function asyncFunction(callback) {
  var sharedVariable = 0;

  setTimeout(function() {
    sharedVariable++;
    callback(sharedVariable);
  }, 1000);
}

asyncFunction(function(value) {
  console.log(value);
});