Question

我想知道在Node.js中使用异步库时如何处理依赖项，请看以下示例：

db.open(function(error, client) {
  client.collection(('my-collection', function(error, collection) {
    collection.insert({ "email": "test@gmail.com" }, function(error, docs) {
      // Do stuff.
    });
  });
});

使用async library：

async.parallel([
    function(callback) {
       db.open(function(error, client) {
         callback(error, client);
       });
    },
    function(callback) {
       // How do I access the "client" variable at this point?
    }
],
function(results){
   // Do stuff.
});

Answer 1

您正在使用async parallell，它可以同时运行所有功能，并且可以按任何顺序完成。

你可以使用异步瀑布函数，它将varibles从一个回调传递给下一个函数，例如。

    async.waterfall([
    function(callback){
        callback(null, 'one', 'two');
    },
    function(arg1, arg2, callback){
        callback(null, 'three');
    },
    function(arg1, callback){
        // arg1 now equals 'three'
        callback(null, 'done');
    }
], function (err, result) {
   // result now equals 'done'    
});

或者你可以使用自动功能，它允许你指定哪些其他功能必须先完成，例如

async.auto({
    get_data: function(callback){
        // async code to get some data
    },
    make_folder: function(callback){
        // async code to create a directory to store a file in
        // this is run at the same time as getting the data
    },
    write_file: ['get_data', 'make_folder', function(callback){
        // once there is some data and the directory exists,
        // write the data to a file in the directory
        callback(null, filename);
    }],
    email_link: ['write_file', function(callback, results){
        // once the file is written let's email a link to it...
        // results.write_file contains the filename returned by write_file.
    }]
});

所以你能做的就是：

async.auto({
    dbReady: function(callback) {
       db.open(function(error, client) {
         callback(error, client);
       });
    },
    connected: ['dbReady', function(callback, results){
       // How do I access the "client" variable at this point?
       console.log(results.dbReady);
    }
},
function(results){
   // Do stuff.
});

Have a look at this to see all the available functions and their uses

节点js异步模块系列依赖项

1 个答案: