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I'm just a beginner in JavaScript, and I would like to wait for the end of an action before executing the next one. I've already searched an answer to my problem on Google, but all I've found are the using of callbacks to string functions together. OK, but that is not what I need. I don't want to make a chain, I want to make an imbrication, like this :

function f1() { function f2() { function f3() { return result; } return result; } return result; }

So that, when I call console.log(f1), it prints the results which is calculated in f3(). Is there a simple way to do this ?

Thank you.

Sara.

EDIT: Well, I think I have to give a better example ! In concrete terms, I work on a web server with express and a a database with mongoose and mongodb. I have four types of path : path concerning jobs, groups, workers and users. When I get a page, I have to get the right list of elements in the database to display : if I go on the page /job, I get the list of existing jobs, if I go on the page /user, I get the list of existing users, etc. In the routing file, I call another file which will manage the connection to the database. Here are my codes :

In the file route.js :

var mongo = require('./mongo'); exports.list = function(req, res) { var data = mongo.read(req.params.type);//the type of element we are looking for (jobs, user...) res.render('liste', { table: data; //In the view, we get table.name, table.status, for each element of the table } }

In my mongo.js :

exports.read = function(type) { var result; start(); //It's the function which start the database, create the schemas, etc... if(type == 'job')//4 conditions, in which we get the right model (in the var model) according to the page we're looking for model.find(function(err, data) { if(err) { ... } else { result = data; } } return result; //It return nothing, because it do this before doing the model.find(...) }

I hope it is clearer.

EDIT (again...) : Thank you everybody for your answers and thank you Sagi Isha for giving me the solution :)

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    This code as is makes little sense, since no function is ever executed. Can you provide a better example? Commented May 23, 2013 at 8:17
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    I think it might be helpful if you could provide a more concrete example of what you're trying to achieve. At the moment I'm not sure what should be happening here. Commented May 23, 2013 at 8:22
  • A function call always wait for it to return: var a = myfunction1(myfunction2()); The result of myfunction2 is passed to myfunction1 and then variable a is set with the result. Callbacks are used for asynchronous execution such as timeOut and ajax calls but I don't see that in your code. Commented May 23, 2013 at 8:22

5 Answers 5

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according to your node/express code: Node work asynchornocally, which means you need to pass callbacks to I/O operations,

i.e 

var mongo = require('./mongo'); exports.list = function(req, res) { mongo.read(req.params.type, function(err, data){ if (err) {return console.error(err)} res.render('liste', {table: data}); }); }

and

exports.read = function(type, callback) { if(type == 'job') { model.find(callback); } }
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6 Comments

I don't think he wants f1()()(). Please do not provide code without further explanation!
That radical change doesn't make it better…
function(f1) or function f1() {}?
Oh ! Thanks ! It works great ! I'm still a little lost with the callbacks so I did not think I could do it that way. If I had enough reputation, I would vote this answer up :)
sure, I would refactor the code a bit so mind it just as a guideline, I would use an MVC pattern in this case, you might find CompoundJS or LocomotiveJS useful to make your application more organized
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In your exemple you never call the functions f2 and f3

function f1() { function f2() { function f3() { return result; } return f3(); } return f2(); }
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as HRM says in comments "A function call always wait for it to return"
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You are looking for the Immediate function invocation :

check this code 

function f1(){ return (function(){ return (function(){ return 1})() })() }; console.log(f1());// prints 1

check this link for more info

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Why that? Why not just function f1() { return 1; }? Those IEFEs seem useless, please explain them.
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We would really need to know what is being done within each function but but assuming you are processing the return value of each function in the next function you could do this:

function f1(){ var inputValue = 1; var result = f2(inputValue); result = f3(result); return result; } function f2(input){ <!-- Do some processing --> return result; } function f3(input){ <!-- Do some processing --> return result; }
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It sounds like you are having asynchronous code - the functions do return before they yield their result to a callback function:

function async(callback) { // start heavy processing return undefined; // when processing is finished, // callback(result); }

Examples are setTimeout, ajax, user events etc.

If you have such behaviour in your code, you will need to pass the nested f2/f3 as callbacks to them:

function f1(callback) { someAsync1(function f2(resultfromAsync1) { someAsync2(function f3(resultfromAsync2) { someAsync3(callback); }); }); });

To call that and log the result, you will use

f1(function(resultfromAsync3) { console.log(resultfromAsync3); });
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