Assign global variable from async.waterfall

Question

How could I assign value to a global variable from async.waterfall that is inside of setTimeout?

Here is a part of my code:

var theVar = null;

setTimeout(function () {
 async.waterfall([
      function (next) {
        var thedata = 1;
        next(null,thedata);
      },
      function (thedata,next) {
        if (thedata === 1) {
            theVar = 2;
        }
        theVar = 3;
        next();
 ], function (err, result) {

 });
}, theVar * 1000); //theVar is timeout here.

So, basically, I want to set global variable from within async.waterfall. That variable theVar will then be the timeout in setTimeout. Now theVar is always null.

score 0 · Accepted Answer · edited May 23 '17 at 11:52

You can't.

Leaving aside the usual issues of returning from an asynchronous call…

You are trying to do some pretty serious time travel here.

After X seconds, you will start an asynchronous function. At some point after that you will get a value out of it. Only then will you know what X should be.

That's impossible (due to the limitations of causality in general rather than programming specifically).

What would be possible would be to:

Store the current time
Start an asynchronous function
When you got a result from that function, use it to determine an interval
Subtract the difference between "now" and the stored time from the interval
Set a timeout to do something else using that computed time

Of course, since you can't predict the time between steps 2 and 3, it is possible that the value you get in step 4 will be negative (i.e. that the time you would have wanted to run the function will have passed while you waited for the async calculation to finish).

But would it be possible to wrap setTimeout in another setTimeout? Where the wrapped setTimeout assigns `theVar` to the outer setTimeout? — user1665355, Dec 04 '15 at 21:45

Assign global variable from async.waterfall

1 Answers1