如何在for循环节点js中调用asyn函数

Question

I want to call async.parellel([],function(){}) inside a for loop. When i tried the for loop completes execution before the async function execution.How to resolve this problem.

Answer 1

You cannot solve the problem, for it is not a problem, it is how async functions work.

If you start a bunch of async functions during the loop, the latter executes as a whole and puts the formers on the loop to be executed once it releases the control of the flow.

Because of that, you'll see probably the function containing the loop terminates before the async functions start.

The usual approach to give a response to the caller once all the async functions have terminated is by using a callback function as a parameter of the one that contains the root, thus nicely handle the async ones and invoke the callback once all of them have returned.

Answer 2

I agree with Yelizaveta Gagarina.

You can do some stuff like that if you want to work with your for loop:

var fns = [];

for (var i = 0; i < 9; i++) {
  fns.push(function(callback){
     // do stuff here and call your callback with or without error
     callback(null, stuff); // no err in this example
  });
}

async.parallel(fns, function(err, stuff){
    if(err) return cb(err); // in this example err is null
    // do stuff, call next middleware if you are in this case
    next();
});

There is also async.series if you want to execute some functions 1 per 1. Hope this helps you.