在promise中使用和设置全局变量是不好的做法

Question

通常需要在稍后的步骤中使用从某个承诺返回的某些信息。一个例子是数据库连接：

database.connect()
    .then(dbConnection => runStepOne(dbConnection))
    // runStepOne is async and needs db
    .then(returnValOfStepOne => runStepTwo(returnValOfStepOne, dbConnection))
    // runStepTwo needs both stepOne's return value and db - this is totally reasonable
    // but dbConnection is not available here anymore

为了避免这种情况，我通常会这样做：

var db;
database.connect()
    .then(dbConnection => db = dbConnection)
    .then(() => runStepOne(db))
    // access global
    .then(returnValOfStepOne => runStepTwo(returnValOfStepOne, db))
    // access global again

问题是，这是对还是错？这个问题有更好的模式吗？