使用Bluebird保证功能 [英] Promisifying a function with Bluebird

问题描述

我是javascript异步概念的新手，来自C ++背景.最近，我意识到我的某些功能不起作用，因为它们不返回承诺.

I am new to javascript asynchronous concepts and come from a C++ background. Recently, I realize that some of my functions do not work because they do not return promises.

例如，此功能；

var CSVConverter=require("csvtojson").Converter;

function get_json(cvs_file_location)
{
    var data=fs.readFileSync(cvs_file_location).toString();
    var csvConverter=new CSVConverter();

    csvConverter.fromString(data,function(err,jsonObj){
        if (err){
            console.log("error msg: " + err);
            return null;
        }

        var json_csv = clone_obj(jsonObj);
        console.log(json_csv);
        return json_csv;
    });
}

如果我尝试根据函数的返回值分配变量，则会无法定义.

If I try to assign a variable based on the function's return value, I get undefined.

var alerts_obj = get_json(testData);

如何修改get_json()以返回承诺?我想使用蓝鸟.我正在阅读诺言，但对于初学者而言，这真是令人不知所措.

How can get_json() be modified to return promises? I would like to use Bluebird. I am reading up on promises but it is rather overwhelming at the moment for a beginner.

推荐答案

如果您使用的是bluebird，则只需使用承诺与 promisifyAll():

If you're using bluebird, you can simply use Promisification with promisifyAll():

var Promise = require('bluebird');
var Converter = Promise.promisifyAll(require("csvtojson").Converter);

发挥功能

function get_json(cvs_file_location) {
    var data=fs.readFileSync(cvs_file_location).toString();

    return new Converter().fromString(data)
        .then(function(jsonObj){
            var json_csv = clone_obj(jsonObj);
            console.log(json_csv);
            return json_csv;
    })
        .catch(function(err) {
            console.log("error msg: " + err);
            return null;
    });        
}

编辑您的第二条评论:

您将执行以下操作以获取值:

You would do something like this to get the value:

get_json(cvs_file_location).then(function(val) { console.log(val) }

但是您不能直接将其分配给变量，因为它是异步的. 在此处查看此问题和答案以获取更多见解:如何返回价值来自异步回调函数?

But you can't assign it to a variable directly, as it is asynchronous. See this question and answer for more insights here: How to return value from an asynchronous callback function?

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