node.js - 使模块异步-nodejs

Question

我有以下函数，我将其导出以通过 async.series 方法在其他地方使用。但是，当我在 IDE 的调试器中运行 apiCaller._get 时，它会在执行 get 请求之前返回 undefined。尽管如此，get 请求还是被执行了。然而`apiCaller._get不是异步的，我知道它需要回调，但是我不明白在哪里调用回调。

var http = require("http");
var querystring = require("querystring");
var _ = require("underscore");

apiCaller = {};

apiCaller.token = null;

var server=http.createServer(function(req,res){});

server.listen(8080);

apiCaller._get = function (context, config, TheCallback) {

    // get the parameters for our querytring
    var oauthParams = _.pick(config, "client_id", "client_secret", "grant_type");

    // create the querystring
    var params = querystring.stringify(oauthParams);

    var options = {
        method: "GET",
        hostname: config.host,
        path: "/my/path/to/token?" + params,
        headers : {
            'Content-Type': "application/json",
            'Accept': "application/json"
        }
    };

    var _callback = function(response) {
        console.log('STATUS: ' + response.statusCode);
        console.log('HEADERS: ' + JSON.stringify(response.headers));
        var str = '';

        //another chunk of data has been recieved, so append it to `str`
        response.on('data', function (chunk) {
            str += chunk;
        });

        // error response
        response.on("error", function (error) {
            if ( !context ) {
                console.error("Something went wrong with the api response.");
                return;
            }
            context.done(new Error("Something went wrong with the api response."));
        });

        //the whole response has been recieved, so we just print it out here
        response.on('end', function () {

            apiCaller.token = JSON.parse(str).access_token;
            // we want to stop the request if token is not correct
            if ( !apiCaller.token || apiCaller.token === undefined || apiCaller.token === null ) {
                if ( !context ) {
                    console.error("Something went wrong with the token. Wrong token! Token: %s", apiCaller.token);
                    return;
                }
                console.error("Token: %s", apiCaller.token);
                context.done(new Error("Something went wrong with the token. Wrong token!"));
            }
            console.log(str);
            console.log(apiCaller.token);

        });
    };

    var request = http.request(options, _callback);

    request.on('error', function(e) {
        console.log('problem with request');
    });

    request.end();
};

Answer 1

传入一个函数作为形参TheCallback并在 end 中调用它response 的事件处理程序在 _callback功能。

例如

var _callback = function(response) {
        console.log('STATUS: ' + response.statusCode);
        console.log('HEADERS: ' + JSON.stringify(response.headers));
        var str = '';

        //another chunk of data has been recieved, so append it to `str`
        response.on('data', function (chunk) {
            str += chunk;
        });

        // error response
        response.on("error", function (error) {
            if ( !context ) {
                console.error("Something went wrong with the api response.");
                return;
            }
            context.done(new Error("Something went wrong with the api response."));
        });

        //the whole response has been recieved, so we just print it out here
        response.on('end', function () {

            apiCaller.token = JSON.parse(str).access_token;
            // we want to stop the request if token is not correct
            if ( !apiCaller.token || apiCaller.token === undefined || apiCaller.token === null ) {
                if ( !context ) {
                    console.error("Something went wrong with the token. Wrong token! Token: %s", apiCaller.token);
                    return;
                }
                console.error("Token: %s", apiCaller.token);
                context.done(new Error("Something went wrong with the token. Wrong token!"));
            }
            console.log(str);
            console.log(apiCaller.token);
            TheCallback.apply(context, arguments);
        });

更新:

通过使用 call , apply或bind ，您可以在您选择的上下文中执行回调函数。可能是context提供的对象或您需要的任何其他内容。如果您不需要更改回调执行的 this 绑定(bind)，只需使用 TheCallback () 调用它即可。 .