How to make a function wait until a callback has been called using node.js

The "good node.js /event driven" way of doing this is to not wait.

Like almost everything else when working with event driven systems like node, your function should accept a callback parameter that will be invoked when then computation is complete. The caller should not wait for the value to be "returned" in the normal sense, but rather send the routine that will handle the resulting value:

function(query, callback) {  myApi.exec('SomeCommand', function(response) {    // other stuff here...    // bla bla..    callback(response); // this will "return" your value to the original caller  });}

So you dont use it like this:

var returnValue = myFunction(query);

But like this:

myFunction(query, function(returnValue) {  // use the return value here instead of like a regular (non-evented) return value});

One way to achieve this is to wrap the API call into a promise and then use await to wait for the result.

// let's say this is the API function with two callbacks,// one for success and the other for errorfunction apiFunction(query, successCallback, errorCallback) {    if (query == "bad query") {        errorCallback("problem with the query");    }    successCallback("Your query was <" + query + ">");}// myFunction wraps the above API call into a Promise// and handles the callbacks with resolve and rejectfunction apiFunctionWrapper(query) {    return new Promise((resolve, reject) => {        apiFunction(query,(successResponse) => {            resolve(successResponse);        }, (errorResponse) => {            reject(errorResponse);        });    });}// now you can use await to get the result from the wrapped api function// and you can use standard try-catch to handle the errorsasync function businessLogic() {    try {        const result = await apiFunctionWrapper("query all users");        console.log(result);                // the next line will fail        const result2 = await apiFunctionWrapper("bad query");    } catch(error) {        console.error("ERROR:" + error);    }}// call the main functionbusinessLogic();

Output:

Your query was <query all users>ERROR:problem with the query

check this:https://github.com/luciotato/waitfor-ES6

your code with wait.for: (requires generators, --harmony flag)

function* (query) {  var r = yield wait.for( myApi.exec, 'SomeCommand');  return r;}