nodejs怎么同步从一个数据库查询函数中返回一个值

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var schema1 = new Schema({ name: String });
var schema2 = new Schema({ num: Number});
var conn1 = mongoose.createConnection("mongodb://localhost/A表");
var conn2 = mongoose.createConnection("mongodb://localhost/B表");
var model1 = conn1.model('model1',schema1);
var model2 = conn2.model('model2',schema2);

var assert = require('assert');
var doc1=new model1({name:'doc1'});
doc1.save(function(err){
assert.equal(null,err);
});
var doc2=new model2({num:2});
doc2.save(function(err){
assert.equal(null,err);
});