Function returning before async method done Node JS

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长情又很酷
长情又很酷 2021-01-21 02:15

I currently have a function that is called from my router:

router.js:

var result = Api.getUser();

console.log(\"Result: \" + result);

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3条回答
  • 2021-01-21 02:42

    You are dealing with asynchronous code. There are a couple ways to solve this problem.

    With A Promise

    // api.js
    var Promise = require('bluebird');
    var request = require('request');
    var getP = Promise.promisify(request.get.bind(request));
    
    exports.getUser = function(accessToken) {
      return getP({
        uri: URL + '/user/me/',
        headers: {Authorization: 'bearer ' + accessToken},
        json: true
      }).spread(function(e, r, body) {
        console.log("e: " + e + " body: %j", body);
        if(e) {
          return Promise.reject("{error: true}");
        } else {
          return Promise.resolve(body);
        }
      });
    };
    
    // main.js
    api.getUser(req.user.accessToken)
      .then(console.log.bind(console, "Result: "))
      .catch(console.error.bind(console));
    

    With A Callback

    // api.js
    var request = require('request');
    
    exports.getUser = function(accessToken, callback) {
      request.get({
        uri: URL + '/user/me/',
        headers: {Authorization: 'bearer ' + accessToken},
        json: true
      }, function(e, r, body) {
        console.log("e: " + e + " body: %j", body);
        if(e) {
          callback("{error: true}");
        } else {
          callback(null, body);
        }
      });
    };
    
    // main.js
    api.getUser(req.user.accessToken, function (err, result) {
      if (err) return console.error(err);
      console.log("Result: " + result);
    });
    

    The nice thing about the promise API is that you only ever need to check for errors once, in your final .catch handler. In the callback style if you need to keep making additional asynchronous calls then you'll have to keep nesting callbacks and checking if (err) return console.error(err) in every single callback.

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  • 2021-01-21 02:44

    Promises are awesome, I would suggest looking into them. However, a simple callback will do the trick

    api:

    exports.getUser = function(req, result, callback) {
      request.get({
        uri: URL + '/user/me/',
        headers: {Authorization: 'bearer ' + req.user.accessToken},
        json: true
      }, function(e, r, body) {
            if(e) {
                callback({error: true});
            } else {
                callback(body)
            }
        });
    };
    

    router:

    var result
    Api.getUser(req, result, function (response) {
      result = response
      console.log(result)
    });
    
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  • 2021-01-21 02:44

    You can't return from an async function, you use a callback:

    exports.getUser = function(req, result, callback) {
       request.get({
        uri: URL + '/user/me/',
        headers: {Authorization: 'bearer ' + req.user.accessToken},
        json: true
      }, function(e, r, body) {
            if(e) {
                callback({error: true});
            } else {
                callback(body);
            }
        });
    };
    
    Api.getUser(req, result, function(user) {
        console.log(user);
    });
    
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