Asynchronus function handeling in nodes js

Question

I am facing an issue in printing the two statements, I have two functions

var mongoose = require( 'mongoose' );
var_show_test = mongoose.model( 'test' );

exports.showTest = function(req,res) {
    var jsonString = [];

    var_show_test.find(function (err, testa) {
        console.log("In find");
    });

    console.log("In function");
}

but it is printing the statements in sequence

In function
In find

what i want is to print the statements in sequence e.g

In find
In function

I know it is happening due to asynchronous calling, I am little bit confused about callback functions. how to handle this in order to print the statements in sequence.

Callbacks and async programming in JS are hard to understand if you come from Java for example. Here there is a similar question about asynchronous javascript: http://stackoverflow.com/questions/16336367/what-is-the-difference-between-synchronous-and-asynchronous-programming-in-node — Salvatorelab, Nov 21 '13 at 10:27

MD Sayem Ahmed · Accepted Answer · 2013-11-21T05:45:36.030

2

For starter, if you simply want to log into console, then you can put the second console.log into your callback -

exports.showTest = function(req,res) {
    var jsonString = [];

    var_show_test.find(function (err, testa) {
        console.log("In find");
        console.log("In function");
    });
}

But, if you want to execute a function/method after your find callback executes, then you need to use a closure here -

exports.showTest = (function (callback) {
    return function(req,res) {
        var jsonString = [];

        var_show_test.find(function (err, testa) {
            console.log("In find");
            callback();
        });
    }
})(callbackFunc);

function callbackFunc() {
    console.log('In my callback!');
}

edited Nov 21 '13 at 05:45

answered Nov 21 '13 at 05:35

MD Sayem Ahmed

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what will be in (callbackFunc)? – JN_newbie Nov 21 '13 at 05:44
@Java_NewBie: Passs the function/method name that you want to call inside the `find` callback. I am updating my answer to clarify. – MD Sayem Ahmed Nov 21 '13 at 05:45
When i run it, it prints. In my callback. then error on callback(), then In find. I want to print first "In find" and then "In my callback". I am going to check it again. – JN_newbie Nov 21 '13 at 05:52
@Java_NewBie: You are probably doing something wrong somewhere. It will be better if you can post the code snippet that you are using right now. – MD Sayem Ahmed Nov 21 '13 at 05:54
exports.showEmployeeTest = (function(callback){ return function(req,res) { var_show_test.find(function (err, employeedirectory, count) { console.log("In find"); callback(); }); } })(testCallBack()); function testCallBack(){ console.log("In test call back"); } – JN_newbie Nov 21 '13 at 05:57
@Java_NewBie: You should only pass `testCallBack`, not `testCallBack()` as argument. You only pass the function name, not call the function. – MD Sayem Ahmed Nov 21 '13 at 06:00
Hi Sayem, I have one more issue to discuss, can I post my code here? – JN_newbie Nov 21 '13 at 06:25
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/41592/discussion-between-sayem-ahmed-and-java-newbie) – MD Sayem Ahmed Nov 21 '13 at 06:26

Asynchronus function handeling in nodes js

1 Answers1