Update talib.js - fixed talib callback signature

[metachris]

Fixed callback signature of talib (needs err and result parameters, see https://github.com/oransel/node-talib).

[metachris]

Not 100% sure you can merge it like this.

• How did that work before // was this callback signature introduced in a newer version of talib? Then we should update package.json accordingly.
• Can result still contain the error property?

[askmike]

Hey! The callback signature was changed as part in node-talib 1.0.3. If you manually install 1.0.2 this code will break (as well as everyone who has talib installed already and updates Gekko if this PR is in). I'll leave this PR open for a little bit until I've tested what happens when running this on talib 1.0.2.

[metachris]

I see two ways of dealing with both the legacy talib and the new one:

1. Change this execute method to accept two generic arguments arg1 and arg2 and test them so it works with both the old and new version of talib
2. Have 2 different execute methods -- one for the old talib and one for the new?

What do you think?

[askmike]

what about one proper execute method (the one in your PR), and one method that wraps the proper one and splits the error into it's own argument (in case of old talib verison)?

like so:

const executeCallback = function(err, result) { /* version in your PR */. }
const LegacyExecuteCallback = function(result) {
 var error = result.error;
 executeCallback.apply(this, [error, result]);
}

And we can use the proper one by testing talib.version (in combination with semver for example)?
What do you think?

[metachris]

I think this is a good idea! I'll update the pull request.

[askmike]

great thanks!

[askmike]

I really like the style of composing (wrapping functions in functions), so that if we ever need to do some normalization of output (or input) or whatever, we only have to do that once.