whilst crashes if callback function is not given

[soichih]

Following code

var async = require('async');
async.whilst(
function() { return false; },
function() {console.log('hi');}
);

Will results in

/home/hayashis/git/osg-blast/node_modules/async/lib/async.js:627
            callback();
            ^
TypeError: undefined is not a function

If I don't need to do anything after the loop, it's natural to assume that I should be able to not supply any callback function.

[coreyjewett]

I agree that there is a natural use case for not using the callback. Two reasons I don't think it should be allowed though:

1. This seems like an uncommon use case. I would prefer that Async continue with the current behavior to prevent accidental black holes.
2. If an err is thrown in the test, what happens to it.

I suppose that those are the same issue. Thoughts?

Sent from my Samsung Galaxy S®4

-------- Original message --------
From: Soichi Hayashi [email protected]
Date:02/14/2014 16:04 (GMT-08:00)
To: caolan/async [email protected]
Subject: [async] whilst crashes if callback function is not given (#446)

Following code

var async = require('async');
async.whilst(
function() { return false; },
function() {console.log('hi');}
);
Will results in

/home/hayashis/git/osg-blast/node_modules/async/lib/async.js:627
callback();
^
TypeError: undefined is not a function
If I don't need to do anything after the loop, it's natural to assume that I should be able to not supply any callback function.

—
Reply to this email directly or view it on GitHub.

[soichih]

Humm really? I am really surprised.

All callback functions should be optional unless it's absolutely needed (I can't think of any such case, however). For example, all (as far as I know) callback functions given to node's fs package are optional.

You can do something like...

fs.readFile('test.js');

or

fs.readDir('.');

It might look odd, but maybe user just wants to see if fs.readFile will throw any exception? Who knows.

In case of async.whilst, it is perfectly normal that no post-loop processing is needed. I strongly recommend that you make the last callback function optional to make it more consistent with the rest of the standard node libraries.