同步执行nodejs

如果您正在使用至少7.10版本的Node,则可以使用异步函数和承诺来实现这一点。

// You can return a promise and resolve the promise once connected
module.exports.dbConnection = function dbConnection(collectionName) {
  const MongoClient = require('mongodb').MongoClient;
  const url = "mongodb://127.0.0.1/test";

  return new Promise((resolve, reject) => {
    MongoClient.connect(url, function (err, db) {
      if (err) {
        return reject(err);
      }
      resolve(db.collection(collectionName)); 
    });
  });
}

// You can then call the function within an async function (Node v7.10 and above)
async function fnThatCallsDbConnection() {
  try {
      const collName = await dbConnection('someCollection');
  } catch(e){
    // do something with error
  }
}

let cachedDB;
module.exports.dbConnection = function dbConnection(collectionName) {
  const MongoClient = require('mongodb').MongoClient;
  const url = "mongodb://127.0.0.1/test";

  return new Promise((resolve, reject) => {
    if (cachedDB) {
      resolve(cachedDB.collection(collectionName));
    } else {
      MongoClient.connect(url, function (err, db) {
        if (err) {
          return reject(err);
        }
        cachedDB = db;
        resolve(db.collection(collectionName)); 
      });
    }
  });
}

实现这一点的正确方法是使用回调。接受回调参数,然后在操作完成时将所需信息传递给该函数。

module.exports.dbConnection = function(collectionName, cb)
{
  var MongoClient = require('mongodb').MongoClient;
  var url = "mongodb://127.0.0.1/test";
  var collName;
  MongoClient.connect(url, function(err, db) 
  {
      var collName = db.collection(collectionName); 
      cb(collName); // invoke our callback
  });
}

dbConnection('collName', function (coll) {
    console.log(coll);
    // do something else with our collection
})